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Bài thực hành GIS

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Introduction to the ArcView Interface and the Data, working with tables, inputting Geographical Data, working with tables,... là những nội dung chính trong tài liệu "Bài thực hành GIS". Mời các bạn cùng tham khảo để nắm bắt nội dung chi tiết.

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  1. Practice 1: Introduction to the ArcView Interface and the Data Terms to know.................................................................................................................. 1  ArcView Steps .................................................................................................................. 1  Step 1 Start ArcView.................................................................................................... 1  Step 2 Add a New View to the Project......................................................................... 2  Step 4 Set the Working Directory ................................................................................ 3  Step 5 Create the Project ............................................................................................ 3  Step 6 Add a Theme to the View ................................................................................. 3  Step 7 Turn on the Themes and arrange the draw order ............................................ 4  Step 8 Change the theme symbology ......................................................................... 4  Step 9 Give the Themes and View meaningful names ............................................... 4  Step 10 Zooming in and out ........................................................................................ 5  Step 11 Change the way we see the Europe .............................................................. 5  Step 12 Locating Sheffield (or your area) on the Globe .............................................. 6  In this first practice, you will learn a few important fundamentals about ArcView's graphical user interface (GUI) as well as how to locate yourself on a map. In this first practice you will also become familiar with some of the data that you will be using in later practices. Getting familiar with your data is an important beginning step when using a GIS. These fundamentals will help you be more efficient during the next practices in this project. In this practice you will leam how to open ArcView (version 3.2), start a new project, add a view, and set the working directory (where you save the files that you create). You will also leam how to add themes to a view, turn them on, arrange an appropriate draw order, and change the symbols. In this practice you will take time to get familiar with many of the menus, buttons, and tools that you will use in the next practices. Also, from the next practice, you will also leam how to open an attribute table and perform a simple query. Last, but not least, in this practice you will leam about map coordinates, scale and changing map projections. Terms to know • Shapefile: a file storage unit that ArcView uses. • Theme: the type of data you are looking at. For example, roads, rivers, soil, mountain peaks, or wildemess areas. Each theme will be either a point, line, or polygon shape. Think of it as a "theme of a party!" (The theme ofmy 'point' party is 'mountain peaks'). • Attribute: characteristics about a theme that are contained in a table. Every theme has an attribute table. • Query: when you select a portion of a theme based on an attribute in the table you are making a query. You are asking the table or the spatial data a question. • Coordinates: locations on the surface of earth where a feature is located. Measured in latitude and longitude or decimal degrees. • Feature: one or more features make a theme, for example, one road in the roads theme is a feature. • Projection: a perspective of the surface of the earth that will distort the shape, area, distance, or direction of the features in a theme. • Scale: the units on the ground as compared to the units on the map. For example, a scale of 1:25,000 means that 1 unit on the map equals 25,000 units on the ground. The unit is usually a measure of distance (i.e. inches, feet, miles, meters, or kilometers). ArcView Steps Step 1 Start ArcView To access ArcView from the university server, you need to download ArcView package internally in your computer. The below picture illustrates the procedure to access Arc View: Select Start and then, Application, Academic, Social Science, and finally ArcView GIS .
  2. Practice 2: Working with tables ArcView Steps .................................................................................................................. 8  Step 1 Opening data .................................................................................................... 8  Step 2 Table properties ............................................................................................... 9  Step 3 Adding data to the table ................................................................................... 9  Step 4 Simple table functionality ............................................................................... 10  Step 5 Selecting features........................................................................................... 10  Step 6 The query builder ........................................................................................... 10  Step 7 Creating new tables ....................................................................................... 11  Step 8 Joining tables ................................................................................................. 11  In this practical you will discover how to open, edit, create and work with tables. Firstly, you will need to start ArcView, start a new project, add a view and set the working directory (to 'c:\') as demonstrated in the last practice. An ArcView project can contain any number oftables - to see which tables are in a project click onthe tables' icon in the 'project window'. ArcView Steps Step 1 Opening data Click the Add Theme button. Navigate to the directory for 'c:\arcv32\arcview\esridata\usa'. Select the following theme:- 'states.shp'. Click OK. This theme will now be added to your view. We are going to edit data within the theme and do not want to overwrite the original file and so we will have to make a copy ofthe data. Make sure the 'states' theme is active by clicking on the theme in the legend (the area will appear raised or 3-D). Go to the 'Theme' menu and select 'Convert to Shapeflle' - as illustrated below:- Call the converted theme 'States' and save it to you u directory. We no longer require the
  3. Practice 2: Working with tables ERS 120: Principles of GIS original data - so make the theme active, then go to the 'Edit' menu and select 'Cut Theme.'. Now make the new 'States' theme active and then click on the 'Open Theme Table' button ( ). You should now see all the attribute information relevant for the states theme. Each record (row) represents one state and each field (column) is a variable containing information appertaining to the states. You can use the scroll bars to either scroll down or up to see more records, or scroll right and left to examine the various fields. Step 2 Table properties We are now going to change the table name and edit the fields that are visibl e to us speeding up display of the table within ArcVi ew. Go to the 'Table' menu and select 'Properties'. We can rename the title of the table - let's call it 'American States'. Next, in the visible column click to uncheck all apart from the following: Shape; Area; State name; Pop1990; PopI1997; and Pop90 sqmi. Don't click on the OK just yet. All the other fields will now no longer appear in the table display - although they have NOT been deleted from the database- we just can't see them. Find the field called 'Pop90 sqmi' within the table properties dialog box. Click in the 'Alia.' column next to this entry and type 'Population density 1990'. -Then click OK for your changes to take effect. The field name we changed is now too long to fit within the display properly. We can ext end the size of the field by moving the mouse over the edge of the field name and by clicking and holding the left- mouse button (see figure below), then move the mouse to extend the fields visible area. We can also re-arrange the order of the fields. Click on the name at the top of the column and drag it right or left. This doesn't re- arrange the table itself-just how we see it within ArcView. Experiment by changing the order of the fields. Step 3 Adding data to the table Firstly, we have to start editing the table, go to the 'Table' menu and select 'Start Editing'. To add a field, go to the 'Edit' menu and select 'Add Field'. Type the name of the attribute - in this case 'Pop change' Under 'Type' you can choose the type of data you will be entering: 'Number' for numerical entries; 'String' for text (word) information; or 'Boolean' for true/false entries. We are entering numbers for this field. The 'width' corresponds to the number of characters that can fit within the field, for example 'xxxx' occupies 4 character spaces. Indicate the number of decimal places required - we do not require them so leave it as the default of '0'. Click 'OK' - you should now see your new column added to the right side of the table. Click on the 'Edit' button ( ).We are now ready to enter data into the table. We could do it manually by hand but there are 51 records in this table (shown in the top left hand side ) and so an automated data entry would be much quicker. Make sure the field title (pop_change) is highlighted - it should appear a darker grey than the other field titles), then click on the 'Calculate' button ( ). This will allow us to write an equation that ArcView will solve and enter into the column. We require population change and so double click on the following; 'Pop1999' from the fields list; '-' from the requests; and then on the field 'Pop 1990', Your display should now resemble the figure below. Click on 'OK' to start the calculations. After a few seconds you should see the results fill the 'Pop_change' N.D. Bình 9/59
  4. Practice 2: Working with tables ERS 120: Principles of GIS column. Once finished choose 'Stop Editing' from the table menu and save your edits. Step 4 Simple table functionality We can sort each field either in ascending or descending order using the following buttons ( ). The find record button ( ) can be used to find the first record whose data items contain the input character/numeric string. For example try searching for 'New York' to find the appropriate record. Step 5 Selecting features • a) Select button - use this button to commence 'selection mode' • b) Edit button - click on this to be enable edit mode to input into the table • c) Identify - used to view record fields within vertical viewing box You can select records in the table to work with them. Sort the 'Population_change' field by descending order. Click on California's record (remember you must be in selection mode using the 'Select Button' illustrated at the top of the page) – notice that it is now highlighted yellow - this means the record is selected. If you now look within 'View1' (you may have to minimise the table), the geographical state of California will also be highlighted yellow. We can select multiple records within the table by holding down the 'shift' key while clicking on records. Selecting records can also work the other way round - by selecting states within the view, corresponding records in the table will be highlighted. Click on the 'Select Feature' tool ( ),and then click on a state within the view - the record will now be highlighted within the table. Multiple records can be selected by holding the mouse button when using the 'select feature' tool. Select the states of Alaska and Hawaii (see below) and return to the table. The selected features may not necessarily be visible, so to move the selected records to the top of the table click on the 'Promote' button ( ). If you now click on the 'Switch Selection' button ( ) the highlighted records will be unselected and those that were previously selected will now be highlighted. To select all the records within the table use the 'Select All' button ( ). When you have finished examining the possible ways of selecting records, choose the 'Select None' button ( ) to deselect all records. Step 6 The query builder Feature selection can also be accomplished using an SQL (Structured Query Language) expression using the database fields and values. Click on the 'Query Builder' button ( ) or select 'Query' from within the 'Theme' menu. Double click on the field to query; then single click an operator; and double click on either a value or manually type the required criteria. Options within the 'query builder' include: > Update values: lists and updates all unique values in the chosen field > New set: New selection set - features not m the set are unselected > Add to set: Adds features to existing selected set > Select from set: Selects from existing selected set Use the query builder to select all the states that have suffered a decrease in the population N.D. Bình 10/59
  5. Practice 2: Working with tables ERS 120: Principles of GIS between 1990 and 1997. You can also build a character string query by using double quotations and wildcards (*), for example: Find all states that begin with the letter A ( [Statename1= "A*") Find all states that contain the letter A ( [Statename1= "*A*") Remember to click on the 'New Set' button to create a new selection or 'Add to set' to add this new query to a previous query selection. Experiment using the two different options (for example select all states beginning with "A" using a new set, and then add all stat es beginning with "N"). Try these examples and think of some for yourself. Once you have finished experimenting with the query builder and the use of wildcards - use the 'Select None' button to clear selected features from both the database (table) and graphical (the VIew) displays. Step 7 Creating new tables To create a table from scratch - click on the 'new' button within the 'project window ' and create a new table called 'cities' in your c directory. Once the blank table has opened click on 'Add Field' within the 'Edit ' menu. Repeat to create the following fields: Now go to the 'Edit ' menu and select 'Add Record'. Repeat this to enter the following information (note ArcView is case-sensitive so us e capital1etters exactly as shown below): Step 8 Joining tables You can join a second table to the active table, based on the values of a common field found in both table s. Joins establish a one-to-one, or many-to-one relationship between the destination N.D. Bình 11/59
  6. Practice 2: Working with tables ERS 120: Principles of GIS table (the active table) and the source table (the tab le you are joining into the active table). Typically, the source table contains descriptive attributes of features that you wish to join into a themes table so that you can symbolise, label, query and analyse the features in the theme using the data from your source table. Joins can be accomplished using any data type (String, Number, Boolean or Date). We are now going to join the ' states' and ' cities' tables. Open the ' states' table and then click on the 'State _name' field header (see figure 1 below), then open the ' cities' table and select the 'State_name' field header (see figure 2). Note how now the 'Join' button ( ) is no longer greyed out - click on it. If the 'Join' button is not available then it is most likely because one of the tables is still being edited. The two table s should now be joined - as illustrated within figure 3 below. Notice how the relevant 'states' attributes have now been added to the 'cities' table. The tables have not been physically linked and the results are only visible in this form within ArcView. To save the new table it either has to be exported and re-imported; or add new fields and use the 'calculator' to input the information. To return the table to its previous form select 'Remove All Joins' from the 'Table' menu. You can now close ArcView - there is no need to keep any of the files you have created within this practical. The use of 'spatial' joins will be examined in next practical session – where by joins are instigated not by common fields within tables but by features occupying the same geographical area within the view display. In this practical you've seen how it is possible to open, edit and save a table associated with a theme, highlight records in either a table or a view, how to query a table and see how to join tables based on linking common fields. We will use these principles later to promote geographical knowledge. Last modified: Oct 25, 2009 ERS 120: Introduction to Geographic Information Systems / N.D. Bình 12/59
  7. Practice 3: Inputting Geographical Data ArcView Steps ................................................................................................................ 13  Step 1 Point data ....................................................................................................... 13  Step 2 Line data......................................................................................................... 14  Step 3 Polygon data .................................................................................................. 15  Step 4 Digitising using real data ................................................................................ 16  In this practical you will discover how create your own geographic data - including; points; lines; and polygons. Firstly, you will need to start ArcView, start a new project, add a view and set the working directory (to 'c:\'). ArcView Steps Step 1 Point data To create a new theme, go to the 'View' menu and select 'New Theme' – as illustrated below. From the resulting menu it is possible to create either a point; line; or polygon theme (see below). We will begin by creating a 'Point' theme. You will then be asked for the location you wish to create the new theme in and the name of the resulting theme. Select the following location:- 'c:\point_trial'. The theme has now been created but currently holds no information. The theme's drawing Point_trial.shp check box has a
  8. Practice 3: Inputting Geographical Data ERS 120: Principles of GIS dashed line around it ( ) - indicating that it is in editing mode. To activate the pull down list hold the mouse pointer over the small arrow in the bottom right-hand comer and hold down the mouse-button. From the 'Drawing tool palette' that appears (see diagram to the right) make sure the 'Draw Point' tool is selected. Now click within the view to create a point feature. To add attribute data to the points - click on the 'Open Theme Table' button ( ). When you create a new point feature, a corresponding new record is automatically added to the themes feature attribute table. While editing a theme - the table is also in edit mode and so we can add data at anytime. Give your points unique IDs (label them numerically, 1 ... 2 ... 3 ... etc.). Once you have finished close the table window and return to the main view. We have now finished creating our point theme, so we can stop editing. Go to the 'Theme' menu and select 'Stop Editing' (see diagram below). Save your editing. Note how the last created point becomes highlighted - click on the 'Clear Selected Features' button ( ) to nullify this. Note if you now go back to the 'Theme' menu the 'Stop Editing' button has become' Start Editing'. We do not wish to make any new changes to out theme so we can leave the 'Theme' menu (click off the menu area). Step 2 Line data Now repeat the processes descried in step one to create the following line theme' c:\line_trial'. Note how the 'Drawing tool palette' automatically selects the 'Draw Line' function. Click the mouse button over the view and then move the mouse to a new location - a line will appear, click the mouse again and repeat the process. To end a line double click the mouse button. Practise creating lines. When finished , you may want to use the 'Pan' tool to move the viewable area to a new, empty location. N.D. Bình 14/59
  9. Practice 3: Inputting Geographical Data ERS 120: Principles of GIS Right click anywhere within the view and hold the mouse button - the editing popup is now displayed (see diagram below). From here snapping options can be chosen - select 'Enable General Snapping' and a new tool called 'Snap' ( becomes available. Now click and hold the left mouse button anywhere in the view - when you now move the mouse a graphic circle will be drawn. This circle represents the extent that a line will be 'snapped' to another line. Set the snapping distance to approximately 3 cm on your display. When you now draw a line the graphic circle will be attached to the end of the line. Draw a line as depicted below and then begin to construct another as illustrated. Normally these lines would not be connected together but because the second line lies within the snapping extent ArcView automatically joins the two lines together. Experiment with the snapping environment. If at any time you want to delete the last waypoint created for a line bring up the editing popup menu and select 'Delete Last Point'. Try it. Remember to end editing mode (Theme - Stop Editing) once you have finished and save your edits. Step 3 Polygon data Repeat the processes descried in step one to create a new polygon theme - 'c:\poly_trial'. Your polygons can be simple rectangles (use the tool, click and hold the mouse button and then move to a new location before releasing the button), circles -use the same methodology as for rectangles), or irregular . Note you change the type of polygon by initiating the 'Drawing tool palette' (hold the left mouse button while over the current drawing tool (for example ). Irregular polygons are created in the same manner as lines, whereby the user clicks to assign way points and double clicks when finished. Try and create a mixture of polygons. You can alter your polygons using the 'Split' and the 'Adjacent' functions found within drawing tool palette. Samples of what they do are illustrated below - experiment with them for yourself. N.D. Bình 15/59
  10. Practice 3: Inputting Geographical Data ERS 120: Principles of GIS Again general snapping can be used to create polygons that share mutual boundaries (similar to the adjacent tool). Experiment by creating a mosaic of polygons that fill the view, similar to that displayed below. Once you have finished you may wish to delete the themes you have created to save space - note you will have to delete them from your view (Edit - Delete Themes) before deleting the actual files is possible. Step 4 Digitising using real data The majority of themes that require digitising with usually require raster to vector conversion. Here we will rectify a pre-scanned image of Sheffield and then digitize certain features. To geo-reference the image - minimise ArcView, open 'Notepad' (found within the 'Start menu', 'Programs' and then 'Accessories') and type the following:- 11.48373502851803 0.0 0.0 -11.48373502851803 433091 N.D. Bình 16/59
  11. Practice 3: Inputting Geographical Data ERS 120: Principles of GIS 390912 Save the file as 'c:\temp\backdrop'. However, the file will automatically be saved as a text document but we require it to have a *jpgw extension. So, go to 'Command Prompt' for MS DOS ('Start menu' then 'Programs') and type the following:- cd\ cd temp rename c:\temp\backdrop.txt backdrop.jpgw exit 5 Return to ArcView, to make a jpeg image visible we firstly have to load the appropriate extension. Go to the 'File' menu and select 'Extensions ', check the box next to the 'JPEG (JFIF) Image Support' extension. Now open the image ('add theme') 'c:\temp\backdrop.jpg', remembering that it is an image data source that we require. To check if the image is correctly rectified open up the feature theme 'c:\temp\roads.shp' the roads should align with those within the backdrop. Digitise the railway within the backdrop by creating a new line theme call it 'c:\airway.shp' . Open up the theme ' c:\temp\wards.shp'. Digitise the polygons and points as separate themes (entitled 'c :\wards.shp' and 'c:\points.shp' respectively). Overlay all the relevant vector shape themes (railway, roads, points and wards) with the backdrop image to display the finished dataset (you should have something like that shown below). Once finished, there is no need to keep any of the files you have created. This week you have learnt how to create graphical features and also how to perform basic 'heads-up' digitising within ArcView. When these techniques are combined with the creation of tabular attribute data (as demonstrated in last practical sessions) it is possible to create a whole database to fulfill your data requirements. Last modified: Oct 25, 2009 ERS 120: Introduction to Geographic Information Systems / N.D. Bình 17/59
  12. Practice 4: Working with tables ArcView Steps ................................................................................................................ 18  Step 1 Opening data and change theme names ....................................................... 18  Step 2 Preparing spatial join ...................................................................................... 18  Step 3 Spatial Join ..................................................................................................... 19  Step 4 Buffering ......................................................................................................... 21  Step 5 Spatial relationship (Select By Theme) .......................................................... 23  This practice extends your knowledge ofhow GIS is used to find new information based on existing data. Perhaps the defining feature of a geographical information system is the ability to analyse data in a spatial context. Other software can handle attribute or even geographical data, however a GIS can take these data and increase your knowledge about the place. This practice covers a few ofthe kinds of analysis that GIS software can do. In this practice, you will be able to: • Relate (join) non-spatial database table to a geographical-based table ('spatial join') • Create buffers for geographic features ('buffering') • Discover the ability to select the features of one or more themes using the features of another theme ('spatial relationship') Firstly, you will need to start ArcView, start a new project, add a view and set the working directory (to 'c: \temp or c:\') as practiced last week. Secondly, you need to open a View using the view icon in the project window in ArcView. Thirdly, you need to add some themes, cities.shp, mjrivers.shp, mjurban.shp and country.shp from the directory, 'c:\arcv32\arcview\esridata\europe\'. This is the same process what you had done in the first practice session. These themes will now be added to your view ArcView Steps Step 1 Opening data and change theme names Since opening all of the four themes in your View window, you can change the view title as 'the United Kingdom' and using 'Legend Editor' and 'Theme Properties' you can name the themes, such as major cities, urban areas, major rivers and all countries. Then, zoom to the UK country using relevant button bars and the View window as illustrated below. Step 2 Preparing spatial join
  13. Practice 4: Working with tables ERS 120: Principles of GIS To perform spatial join in the map, you need to instruct the computer about the relationship between the two themes whether they can be related to each other or not. The key is to identify the feature type between the two themes (i.e. major cities and urban areas). Note that this is a slightly different concept to 'non-spatial tabular join' that requires a common field between an attribute table (dbf, txt or INFO type) and geographical feature. What is mostly different is that they do not need to contain common field. However, they should keep to the rule of spatial feature relationship, such as point-in-polygon. We now need to know the different urbanisation definition of UK major cities. Simply, London and Sheffield are defined as city, however, they has differently defined in the urbanisation categories. To find out this enquiry, you need to use 'spatial join' function in ArcView. Step 2.1. Highlight Common Field in Theme Table At first, you need to open their attribute tables, 'Attribute of major cities' and 'Attribute of urban areas' using the 'Open Theme Table' button ( ). Make sure the urban areas table ('Attribute of urban areas') is active (blue highlight in the title bar). Scroll right if necessary to find the field (column) labelled shape. Click once on the name of this field - the name box should darken to indicate you have selected this field. Step 2.2. Highlight Common Field in another Theme Table Click once on the other table in the project, labelled 'Attribute of major cities '. You can use the Window menu to find it if it is hidden behind other windows. This should activate this table (blue in the title bar). Then, scroll left or right if necessary to find the shape field in this table. Click on its name to select it (become dark). You have now selected the field in each table that has the necessary information to relate the tables to each other. Notice that even though the field names are the same in the two tables (shape), the topological characteristics are different (polygon vs. point). Note it is important to join the tables in the correct order (Join A To B). Step 3 Spatial Join Step 3.1. Point-in-Polygon In the menu, choose Join in the menu bar or the appropriate button ( ); it is important to note that if the join option/button is grayed out, it means step 2.1 or 2.2 above has not been completed correctly - try those steps again). ArcView responds by taking the columns from the urban areas table and copying them into the Attribute of major cities window, to the right of the existing fields. ArcView also closes the urban areas table window since all its data is now in the feature table window. Scroll right in the table window to see the urban areas' information. N.D. Bình 19/59
  14. Practice 4: Working with tables ERS 120: Principles of GIS Now you can examine urban area information about any of the major cities in the UK. To see this, click in the View window and the major cities theme. Then, click on the Identify button ( ) and click on any of the major cities (i.e. London and Sheffield, or other cities in the UK). The information box opens with the data on these cities. You will notice that you can scroll down in the information box to find the population rank ('Pop_rank' field), population class ('Pop_class' field) and type of urbanization (Type_desc' field) on these cities. None of these data are available until you joined the urbanisation table with major city feature table. Question 1. Use the identify tool, find the population rank, population class and type for urbanisation of London, Sheffield, Leeds, Manchester, Birmingham, Edinburgh and Glasgow. To return the table to its previous form select 'Remove All Joins' from the Table' menu. Step 3.2. Point-in-point/line When the spatial join is based on the 'nearest' relationship (i.e., neither of the two themes involved contains polygons and one of them contains points), ArcView adds a Distance field to the destination table. This field is automatically calculated by ArcView and contains the distance to the nearest feature represented in the source table for each feature represented in the destination table. The distance is calculated in the views' map units. The procedure for this spatial join is exactly the same as the previous steps, 2.1 and 2.2. After opening two tables, Attribute of major cities (point) and Attribute of major rivers (polyline), you just need to click once on the name of the shape field on the Attribute of major rivers and then, click once on the name of the shape field on the Attribute of major cities. Each name box should darken to indicate you have selected the fields. Then, choose Join in the menu bar or button ( N.D. Bình 20/59
  15. Practice 4: Working with tables ERS 120: Principles of GIS ) and a new distance field will be shown containing the distance value to the nearest major cities feature from the major rivers theme. The table is illustrated below: This function is very useful to search for the nearest themes or assign the features to their target themes for spatial analysis, such as closest facility sites from customers, searching for optimal delivery routes, biological habitats partitioning and so on. To return the table to its previous form, also select 'Remove All Joins' from the 'Table' menu. Step 4 Buffering To create buffers for graphics or geographical features, you need to set your views' map and distance units, such as decimal degrees for map unit and mile for distance unit. However you can choose your preference. Note that if you choose different unit scales, you have to also apply your units in the buffering distance procedure. Before searing buffering, you need to choose the rivers in Britain using Select Feature button on Tools bar - as illustrate below Click Promote button ( ) to promote the selected records to the .:.l top of the tab le (Attribute of major rivers), you can find the highlighted rivers' information that 9 rivers are selected from total 367 rivers in the table ( ) After specifying the view units and selecting the main rivers in Britain, select Create buffering in Theme menu. ArcView immediately open a buffering window to N.D. Bình 21/59
  16. Practice 4: Working with tables ERS 120: Principles of GIS choose buffering options - as illustrate below From the Create Buffers window, check that the 'features of a theme' is Major rivers and the option, Use only the selected features, is selected. You can press Help button on the window if you want to know more details about this stage. Press next button if you are confident with your options. In the next step, you need to specify the type of buffering, buffering distance and distance units. Type '10' as a specified distance value in the option, At a specified distance and specify 'Miles' as distance units in the option, 'Distance units are'. This means that you will create 10 miles buffering polygon surrounding the main rivers theme. As the final stage, select the barrier type of buffers. If you choose no here, then each buffer will be a single shape. If you choose yes, then a single shape will be created representing all the buffers except if you have chosen multiple rings, which will result in a single shape for each of the rings. For this practice, choose Yes. There are three options for saving your buffers. If you want to add the buffers as graphics in your view, choose 'as graphics in the view' option, or if you want to add the buffers to an existing themes that you choose, select 'in an existing theme' option. However, if you want to add the buffers to a new theme (polygon), you can change the filename of this theme by typing a new name, or by clicking the Browser button. For this practice, choose to create a new theme (c:\temp\river_bujfer.shp). If you want to change the previous options, choose
  17. Practice 4: Working with tables ERS 120: Principles of GIS After clicking on the Finish button, the result of the buffers is illustrated below. If you create a new theme, a new polygon theme is promoted to the top of the View window and moved to a relevant position, such as between major rivers and all countries themes. Question 2. How many major cities for within the buffered river area? You may wish to buffer the major rivers of other European countries and compare your results with those obtained for the UK. Step 5 Spatial relationship (Select By Theme) In this practice, we will analyse spatial relationships between different themes using the Select By Theme option in ArcView. N.D. Bình 23/59
  18. Practice 4: Working with tables ERS 120: Principles of GIS Step 5.1. Polygon-Point In this simple spatial query you need to determine how many urban areas (polygons) are within 10 miles of the major cities in the Europe. Make sure that the urban areas and major cities are displayed in the View then make urban areas active theme and choose Select By Theme from the Theme pull-down menu. Change the options to read as follows: III 'Select features of active themes thai', choose Are Within Distance of, 'the selected features of is Major cities, and 'Selection distance' is 10. These options are illustrated below. Then press New Set button. ArcView selects all urban areas in the Europe that fall within 10 miles of the major cities and highlights these in yellow. Press the Open Theme Table button, , to display the attribute table associated with the urban areas. Finally, press the Promote button, , to promote the selected records to the top of the table. Make a note of the selected urban areas then press the Select None button, , before closing the table. Question 3. You can compare the different distance values in the 'Selection distance' option in the Select By Theme window. Choose 20, 30, and 50 miles and compare the total number of the selected urban areas with those of 10 miles above. Can you count the number of the UK using N.D. Bình 24/59
  19. Practice 4: Working with tables ERS 120: Principles of GIS the Query Builder button? Step 5.2. Polygon-Polygon In our final query, we wish to determine how may urban areas (polygons) fall within the buffers you created in the previous section (if you did not create the buffer polygon due to the selection of a graphic option, create a new theme of the buffers). Once again, this is a two stage processes. First of all, you make urban areas the active theme and choose Select By Theme from the Theme pull-down menu. Change the options to read as follows: Then press New Set Press the Open Theme Table button to display the selected records and promote them to the top of the table using Promote button How many urban areas are selected? You may wish to practice with the other options available within the 'Select By Theme' function. You may now quit Arcview. You do no t need to save any changes to th e project file or save them into your directory preferred such as c:\ or d:\. Last modified: Oct 25, 2009 ERS 120: Introduction to Geographic Information Systems / N.D. Bình 25/59
  20. Practice 5: Advanced Analysis I ArcView Steps ................................................................................................................ 26  Step 1 GeoProcessing - Dissolve .............................................................................. 26  Step 2 GeoProcessing - Merge ................................................................................. 27  Step 3 GeoProcessing - Clip ..................................................................................... 27  Step 4 GeoProcessing - Intersect.............................................................................. 28  Step 5 GeoProcessing - Union .................................................................................. 29  Step 6 GeoProcessing - Spatial Join ......................................................................... 30  Step 7 Spatial Analyst - Find Distance ...................................................................... 30  Step 8 Spatial Analyst - Assign Proximity.................................................................. 31  Step 9 Spatial Analyst - Density ................................................................................ 31  Step 10 Spatial Analyst - Summarise Zones ............................................................. 32  Step 11 Spatial Analyst - Reclassify .......................................................................... 32  Step 12 Spatial Analyst - Map Calculator .................................................................. 33  Step 13 Spatial Analyst - Map Query ........................................................................ 33  In this practical you will discover how to manipulate your spatial data through the use of the GeoProcessing wizard; as well as exploring the main functionality of the 'Spatial Analyst' extension. Firstly, you will need to start ArcView, start a new project, add a view and set the working directory (to 'c:\temp'). ArcView Steps Step 1 GeoProcessing - Dissolve We need to load the GeoProcessing extension - go to the 'File' menu and then 'Extensions'. Put a tick in the box corresponding to 'GeoProcessing' and then click on 'OK'. We mw require some sample dala to experiment with. Add the following theme from the directory 'c:\arcv32\arcview\esridata\usa\ ': 'counties.shp '. You may wish to hide the legend within the view (with the relevant theme active, go to the 'Theme' menu and select 'Hide/show Legend'. We are now going to aggregate the counties boundaries into states. This can be achieved because each county has a corresponding state name within the attribute table. Go to the 'GeoProcessing Wizard' within the 'View' menu. Because we've presently only got one theme open all but the dissolve GeoProcessing option are currently unavailable. Click on the 'Next' burton and then dissolve using the attribute of 'State name'. Save the theme to the following location: 'c:\temp\us state.;' (as seen below), and then click on the 'Next' button. We can now choose the attribute data we wish to keep -highlight 'Area by sum' and finally click on the 'Finish' button. You should mw have a theme that contains the US state boundaries.
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