Lecture ERS 120: Principles of GIS - Practice 4: Working with tables - N.D.Bình

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 Practice 4: Working with tables ERS 120: Principles of GIS N.D. Bình 19/59 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. Practice 4: Working with tables ERS 120: Principles of GIS N.D. Bình 20/59 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 ( Practice 4: Working with tables ERS 120: Principles of GIS N.D. Bình 21/59 ) 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 Practice 4: Working with tables ERS 120: Principles of GIS N.D. Bình 22/59 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 << Back button to avoid unnecessary buffers. Practice 4: Working with tables ERS 120: Principles of GIS N.D. Bình 23/59 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. Practice 4: Working with tables ERS 120: Principles of GIS N.D. Bình 24/59 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 Practice 4: Working with tables ERS 120: Principles of GIS N.D. Bình 25/59 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 /