Spatial Analysis using Vector GIS THE GOAL: PREPARATION:

Size: px

Start display at page:

Download "Spatial Analysis using Vector GIS THE GOAL: PREPARATION:"

Carol Horn
5 years ago
Views:

1 PLAN 512 GIS FOR PLANNERS Department of Urban and Environmental Planning University of Virginia Fall 2006 Prof. David L. Phillips Spatial Analysis using Vector GIS THE GOAL: This tutorial explores some of the methods of geographic analysis using vector GIS. We will explore several questions: 1. What proportion of the dwellings in each neighborhood of VENBLGIS are within 800 feet of a retail market selling some groceries? 2. What proportion of the dwellings in each neighborhood of VENBLGIS are within 400 feet of a bus line during the day? 3. What proportion of the dwellings in the study area are within a quarter mile of Gordon Avenue Public Library 4. What proportion of the single family units are within a quarter mile of Venable Elementary School? In order to undertake these analytic questions, we need to be able to perform a series of operations. Some of these have already been explored in previous exercises. 1. Joining tables 2. Creating fields in table 3. Computing new values for new fields 4. Selecting features by pointing at them. 5. Spatial Join where two tables (or types of features) are related by their joint location rather than by an attribute value. New techniques will include: 1. Selection by attribute 2. Selection by Location 3. Creating Buffer regions 4. Summarizing Variables in a table 5. Creating charts from tables and creating charts in thematic maps. 6. Creating Reports from tables PREPARATION: Each of the analytic questions above needs additional data before they can be answered. A. The parcel point feature class has land use. But how many dwellings or housing units are there? This information has been assembled) in a new file NewDUS.dbf. We will join this to the parcel point feature class for the analysis. B. Where are the grocery stores? Some information is available from the parcel file. There are land-use codes from the Planning Department and from the Tax Assessor. The Assessor s codes on the commercial side are more detailed. It contains a Use code for Land Use retail grocery stores: 340. There are also two large grocery stores either in the county or outside the study area. All of these parcels have been put in a separate grocery feature class. C. Where are the bus routes? The City and University bus routes serving the study area have been digitized into feature classes for this exercise. D. Which parcels are within which neighborhood? And what do is meant by within? A spatial relationship is implied here. How can the GIS software work to achieve this relate? E. The majority of this exercise is working with the concept of PROXIMITY. We will explore spatial overlaps and buffers around features. F. The exercise will also explore ways of displaying aggregate information, namely total number of dwelling units, for large spatial areas (Neighborhoods). 1

PROCEDURE: 1. Set up your workspace again on your local computer. Be sure that the following feature data sets are in your geodatabase: a. Intersections (Nodes) b. Streets c. Railroads d.

2 PROCEDURE: 1. Set up your workspace again on your local computer. Be sure that the following feature data sets are in your geodatabase: a. Intersections (Nodes) b. Streets c. Railroads d. Neighborhoods e. Study Region f. Parcels g. Parcel Points h. Block Groups i. Census Tracts j. Buildings 2. From the file server HOME2/COURSES/Files copy and paste the \MoreVenBlGISdata\VenableFacilities.mdb geodatabase to your back up location on the server, change the READ-ONLY permissions and then copy it to your workspace on the local computer. 3. In ArcCatalog, be sure you have identified a direct path to your workspace. Take a few minutes to explore your data sets in the PREVIEW mode. Explore both the geometry and the table views for the features sets and shape files. Refresh your memory on what you called some of the fields in the tables. Specifically, what were the fields you created when digitizing the neighborhoods? What kind of code, name etc did you give each neighborhood? 4. In ArcCatalog, COPY AND PASTE the Feature Data Sets for Transport, Facilities and the data table NewDUS from the provided VenableFacilities.mdb to your own. You will notice that once feature data classes are in a geodatabase, you can copy and paste to other geodatabases provide you are either moving entire feature data SETS or you are moving into a SET with the same spatial reference system and domain. 5. Start ArcMap and load one of your previous map documents. If you have been using MAP PROPERTIES and the advanced data source selection of Use Relative Path Names you should have little trouble opening your map documents. If ArcMap cannot find files in your document, it will enter a red! in the SOURCE view of the table of contents. Clicking on that field or going to the Layer Properties dialogue box allows you to re-point the map document to the new file location. 6. You may want to organize your Data Frame by establishing some Layer Groups and placing related layers within the group. Here is an illustration of such a grouping with the layers collapsed. Streets and Railroads are in the Street and Railroad group. Census Blocks, Tracts and Block Groups in the Census Geography etc. Parcels and Neighborhoods are at the top and the layers used most extensively in this exercise. 2

3 7. Add the Bus Routes and Stops, Grocery Stores, Libraries and Elemenary School to your Data Frame and change the symbolism to show the categories of Bus Routes. Try using some dashed lines to distinguish the routes: 3

8. Open the attribute table for VenParcelPoints [or what

button to ADD FIELD and add a DUS short integer field. 9.

Use the Source rather than Display view of the Table of

Add Data command to get the file (You had copied it into

4 8. Open the attribute table for VenParcelPoints [or what ever you named the layer of parcel points], use the Options button to ADD FIELD and add a DUS short integer field. 9. Add the NewDUS data file to the DataFrame. Use the Source rather than Display view of the Table of Contents. Add Data command to get the file (You had copied it into your Geodatabase from the VenFacilities.mdb.) Return to Display View of Table of Contents and JOIN the NewDU table to the ParcelPoint Features: 4

Just as an earlier exercise joined the tax assessment records, here we join the dwelling unit counts per parcel point using the PROP_ID field.

It attributes one dwelling per single family unit, two dwellings to duplexes, the number of apartments in an apartment structure (counts from the real estate assessor) and attributes 10

This shows the number of dwellings on each residential or mixed use parcels. 10.

5 Just as an earlier exercise joined the tax assessment records, here we join the dwelling unit counts per parcel point using the PROP_ID field. The NewDU table contains the number of dwellings on each residential parcel. It attributes one dwelling per single family unit, two dwellings to duplexes, the number of apartments in an apartment structure (counts from the real estate assessor) and attributes 10 DUS of density to Fraternity/Sorority units. Open the attribute table of ParcelPoints. Examine the DUS field in the basic table and in the joined table. This shows the number of dwellings on each residential or mixed use parcels. 10. We will make this part of the basic VenParPoints attribute table by using the Calculate Values functionality. Select the VenParPoints.DUS column, right click and choose Calculate Values: This opens the Field Calculator Dialog box and allows you to select NewDUs.DUS as the values to calculate into VenParPoints.DUS field. If the Calculate Values option is grayed out, then open the EDITOR bar and Start Editing the appropriate source of data for the parcelpoints feature class. 5

6 11. Prepare a Dwelling Unit Map using the DUS field. Save the Map Document; Export the Map in PDF, JPG and EMF formats. TRANSITION: The next step is to determine exactly into which Neighborhood each Parcel falls. We want this Neighborhood attribute to be part of a parcel coverage. We will do this with a spatial join. However one cannot do a spatial join with a table that is already joined to other tables with an attribute join. 12. Revert the symbology of the VenParPoints layer back to a single symbol. 13. Remove all joins to the VenParPoints layer. 14. We are now going generate a SPATIAL JOIN where we ask the software to link the Neighborhood Layer (table fields) to the CityParcel Layer based not on the attribute values, but on spatial location. Begin the process by asking to JOIN a new table to PARCEL Notice that the JOIN is based on SPATIAL LOCATION Neighborhoods are the spatial reference layer Fields will be added to the parcel points table in the join A new feature class within parcel feature data set is created here named VenParPointNeigh This should be added to the Parcel Data Set in your 15. How well did it work? How well did you digitize your Neighborhoods? Create a thematic map using the VenParPointNeigh layer showing the categorical theme of the neighborhood name. Let the Neighborhood Layer provide the label for the neighborhoods, but let the parcels show the quality of neighborhood. 6

Some of the parcels around the periphery of the neighborhoods may not have a neighborhood name.

It did do not lie totally within a neighborhood boundary. This is due to digitized neighborhoods and the parcel layer not being exactly the same.

It helps if the Neighborhoods are LABELLED. 16. With the table for VenParPointNeigh open, Sort on the Neighborhood name field.

7 Some of the parcels around the periphery of the neighborhoods may not have a neighborhood name. For the sample data set, the circled value did not get assigned to a neighborhood by the join. It did do not lie totally within a neighborhood boundary. This is due to digitized neighborhoods and the parcel layer not being exactly the same. The illustration above also shows the parcel lines and shows how ambiguous this neighborhood boundary can be. It helps if the Neighborhoods are LABELLED. 16. With the table for VenParPointNeigh open, Sort on the Neighborhood name field. Notice the blank records at the top. Some of these will be parcel points totally outside of our study region. Survey your map and discover points which are on the boundaries between neighborhoods that were classed as NULL. Use the SELECT TOOL to select them and assign a neighborhood by calculating values or Editing the field. 7

8 17. OPTIONAL: You can do the same operation with the land parcels themselves. Performing the spatial join with neighborhoods will give even more parcels without values for the neighborhood name or code. Reason: There are more apt to be digitizing errors along the parcel boundaries that when simply dealing with points. You can find the Null values in the Parcel table by using a SELECTION BY ATTRIBUTES command. You get a Query Builder. Making a new selection. Parcel Double click on the NAME field name in the left hand window. (or what ever the field is that contains the neighborhood name) With the complete list of values showing in the right window, first single click the IS operator key then double click on the NULL field in the right hand window. The resulting query will be: Name IS NULL This will select all parcels not yet classified. You can have the Table now Show you only the SELECTED RECORDS. HOW MANY PARCELS WERE NOT CLASSIFIED IN YOUR PROJECT? NOTE THIS NUMBER AND REPORT IT. Open the Neighborhood Table for reference to the name and code. Start editing the Parcel layer. And be sure that the editor has activated it. With only the SELECTED records showing in the table, Highlight each record, note what neighborhood it is in and then edit the Fields accordingly. Save edits often. Stop editing when finished and save edits. Alternatively, you may want to EDIT MODIFY the Neighborhood boundaries to more closely reflect the parcel boundaries and the reconstruct Parcel_Neigh feature class and use it make the last minute modifications and continue. 18. The resulting thematic map should have all of the parcels correctly classed into the neighborhoods. CREATE SUCH A MAP FOR NEIGHBORHOOD NAME AND TYPE OR LETTER TO SUBSTANTIATE YOUR EDITING. SAVE A MAP DOCUMENT. EXPORT PDF, EMF, JPG FILES. TRANSITION:The next analytic questions ask what proportion of the dwelling units in each of the neighborhoods are within a certain distance of different features or resources. In order to compute a proportion, you need to know the total. Consequently, the first piece of analysis is to summarize the number of dwelling units (DUS) in each neighborhood. The number of DU s on a parcel is now found in the VenParPoint file and was conveyed to the VenParPointNeigh file. 8

19. Summarize the resulting table on the Neighborhood Letter or type field: The

{ Pay no attention to the man behind the curtain } Here Summarize is performed on the

This simplifies later work that could occur because of misspelling a neighborhood name.

9 19. Summarize the resulting table on the Neighborhood Letter or type field: The neighborhood names are masked here because the illustration comes from a different exercise. { Pay no attention to the man behind the curtain } Here Summarize is performed on the Letter (CODE) that identifies a neighborhood. This simplifies later work that could occur because of misspelling a neighborhood name. Be sure to summarize the DUS field and get the SUM Here output is a TABLE to be stored in the geodatabase. Here named SumDUS Find the table and Open It. 9

Notice that there is a <Null> field remaining. This is because there are numerous points outside the study area and do not fall in any neighborhood.

The first analytic question is what proportion of the dwellings ware within 800 feet of a retail grocery Market.

10 Notice that there is a <Null> field remaining. This is because there are numerous points outside the study area and do not fall in any neighborhood. (If you get a SUM_DUS of Zero, edit the 0 so that it is just 1. This will avoid future computation problems like dividing by zero.) 20. The first analytic question is what proportion of the dwellings ware within 800 feet of a retail grocery Market. The Grocery stores have already been identified and you have added them into the parcel feature data set. 21. If the Buffer Wizard is not already in the TOOLS menu, we will need to add a BUFFER WIZARD TO THE INTEFACE: (following the ArcMap HELP: How to add the Buffer Wizard to the Tools menu 1. Click the Tools menu and click Customize. 2. Click the Commands tab. 3. Click Tools in the Categories list. 4. Click Buffer Wizard in the Commands list and drag it to the Tools menu on the Main menu. The Tools menu will open and you can drop it within the menu at any location. Optionally, you can choose to place the Buffer Wizard on any of the menus or toolbars you wish. Click Close on the Customize dialog box. To establish the region within 800 feet of these stores, use the Buffer tool: TOOLS BUFFER WIZARD: 10

Be sure that Buffers are Built only on grocery

11 Be sure that Buffers are Built only on grocery features Here specify the radius of the Buffer and be sure the Units are in Feet! Yes, do merge the buffers Outside the parcels Be careful where you save it. Give it a specific name. And place it in a Feature Data Set Facilities 11

The resulting buffers will be added to the data frame.

Clear the Selected Features of VenParPointNeigh

12 The resulting buffers will be added to the data frame. Symbolize them. You should get something like the diagram to the left. 22. Now find all parcelpoints that intersect with the buffer. Clear the Selected Features of VenParPointNeigh (SELECTION CLEAR SELECTED FEATURES) Use the SELECT BY LOCATION tool: We want to select parcels from Par_Neigh 12

HOW MANY PARCELS WERE SELECTED? (I got 606) 23.

13 That intersect. But take a moment to review the many options. Specify the Buffer layer as the overlay. The Resulting Selection shows those parcels (from VenParPointNeigh) which have at least some portion of their area touching or within the Buffer around the Markets. HOW MANY PARCELS WERE SELECTED? (I got 606) 23. Perform a summarization of the Neighborhood Letter field to get the sum of the DUS for the Selected features of VenParPointNeigh: This is similar to step 14 above: The Letter field (or one that was used in step 14) is summarized DUS are Summed The new result table is stored.. here in analysis as SumGROC BUT for SELECTED records ONLY. That is, for only those within the buffer. Result would be something like: 13

Notice that neighborhood 3 did not have any parcel points in the grocery (market) buffer and hence no counted dwellings.

The results will have to become part of the Neighborhood Table. Open the neighborhood attribute table and add four fields: DUTOT, DUMARK, DUNOMARK and MARKPROP.

Join the SUMDUS table and also the SUMGroc tables to the Neighborhood table using the neighborhood Letter or Number (here ID). (This Join is not illustrated here.

14 Notice that neighborhood 3 did not have any parcel points in the grocery (market) buffer and hence no counted dwellings. [Your figures may vary slightly because of the neighborhood boundary differences.] 24. Let us work toward displaying the results on the map of the neighborhoods. The results will have to become part of the Neighborhood Table. Open the neighborhood attribute table and add four fields: DUTOT, DUMARK, DUNOMARK and MARKPROP. The first three can be Integer, the last FLOAT. Domain Values should be set to 0 (zero) 25. Join the SUMDUS table and also the SUMGroc tables to the Neighborhood table using the neighborhood Letter or Number (here ID). (This Join is not illustrated here. It is similar to other joins done in the past. The Neighborhood.Letter field or number field is used as the Joining Field; the SUMDUS is the file and Letter its joining field. Etc). <Null> Values may exist if there were no parcels in the buffer in a particular neighborhood.) 14

Sum_DUS] in the Field Calculator Dialog Box: Use the double click method rather than typing in the variable name.. [ ] are important.

15 Now transfer the values from the joined tables to the new fields of the Neighborhood table 26. For the DUTot field CALCULATE a value and set equal to [SUMDUS.Sum_DUS] in the Field Calculator Dialog Box: Use the double click method rather than typing in the variable name.. [ ] are important. 27. For the DUMark (dwelling units close to Markets), CALCULATE and set equal to (or similar named variable if you used a different name) 28. For the DUNOMARK calculate the difference between DUtot and DUMark. 29. For the MarkProp calculate: 15

30. Once the computations are completed, you can remove all joins from the Neighborhood layer. 31. Map these performance measures for the neighborhoods.

16 30. Once the computations are completed, you can remove all joins from the Neighborhood layer. 31. Map these performance measures for the neighborhoods. The Market Buffers are given 35% transparency. The Neighborhood theme is displayed as PIE CHART with the Light being the DUNoMark dwellings and the Dark DUMark. The SIZE of the Chart is DUTOT. 16

32. Create a REPORT of the results using a report

It is not very user friendly, but can save you some work.

sure to sort on one of the major identifier fields like the

17 32. Create a REPORT of the results using a report generator: (This step may be deferred if you find it to be taking an inordinate amount of time.) This is a crude and quick report generator. It is not very user friendly, but can save you some work. Identify the fields you wish to summarize in the report Be sure to sort on one of the major identifier fields like the name of the neighborhood. Specify any summary information you wish to have calculated as part of the report: 17

In the DISPLAY TAB there are numerous fields to adjust to get the column width, text name as opposed to the variable name displayed, the orientation of the paper, etc etc.

18 In the DISPLAY TAB there are numerous fields to adjust to get the column width, text name as opposed to the variable name displayed, the orientation of the paper, etc etc. A lot of tedious but useful things to work through. There is a nice preview option. Finally you can get a GENERATED report that looks something like: This report can be printed, exported or saved. Please export a pdf version for submission. There is also a Crystal Report Wizard which may work better, but is much more complex. 18

19 TRANSITION to going it alone: The remainder of the exercise involves repeating steps similar to 20 through 32 for some other features in the neighborhood. What proportion of the dwellings in each neighborhood of VENBLGIS are within 400 feet of a bus line. For the buses build 400 foot buffers, select the features of VenParPointNeigh that intersect the buffer and summarize the Neighborhood.CODE for the Sum of DUS and save the resulting table. How many Parcels were selected? Create new fields in the Neighborhood Table, join the summary table for buses and calculate new values for number of dwellings served by bus, the number not served and the proportion served. Display on a map. Perhaps write a report What proportion of the Study Area s dwellings are within ¼ mile of the Gordon Avenue Library? What proportion of the Study Areas s single family dwellings are within ¼ mile of Venable Elementary School? Optional: What if you used different buffer radii? PRODUCTS: 1. A map showing the number of dwellings on each parcel. 2. A map of the parcel points showing by color or pattern which neighborhood they are in. Label the map with neighborhood name, but do not shade the neighborhoods. Let the parcel points display the neighborhood tone. 3. (Optional) A map of the parcel points showing by color or pattern which neighborhood they are in. Label the map with neighborhood name, but do not shade the neighborhoods. Let the parcel points display the neighborhood tone. 4. A map of the Markets and Buffer. 5. A map of the proportion of each neighborhood dwellings served by Markets. 6. A map of the Bus Routes and 400 foot service buffers. 7. A map of the proportion of each neighborhood dwellings within the Bus Buffer. 8. At least one Summary report. 9. A map of the parcel points within ¼ mile of the Gordon Avenue Library 10. A map of the parcel points within ¼ mile of the Venable Elementary School. 11. Reflections on the exercise. Include in your Reflections the number of parcels selected at different portions of the exercise as a way to check your work and reflect on why they may differ from other student s work. DUE DATE: Finished October 17 (A Tuesday). We will be working on this exercise this week and a good part of next. We will have a short address matching exercise next week and begin a Raster Analysis exercise on the 19 th. This is a long exercise. Detailed. Get an early start. 19

In this exercise we will learn how to use the analysis tools in ArcGIS with vector and raster data to further examine potential building sites.

In this exercise we will learn how to use the analysis tools in ArcGIS with vector and raster data to further examine potential building sites. GIS Level 2 In the Introduction to GIS workshop we filtered data and visually examined it to determine where to potentially build a new mixed use facility. In order to get a low interest loan, the building