The MCHP GIS MANUAL - Selecting Data: By Location

         

Introduction   Contents


 USING ArcGIS: 
   
1. Basic Use of ArcMap 
   Creating a Map 
   Data Frame Tools
   Data Frame Properties
   Tables and Charts
   Layout View
   Saving Map Documents
   Activity 1

2. Map Projections
   Projections
   UTM
   Datums
  
3. ArcCatalog 
   Basic Uses    
   
4. ArcToolBox 
   Basic Uses    
   
5. Adding Spatial Information
   Georeferencing
   Adding Non-Spatial Data
   Dbase Files
   Activity 2

6. Selecting Data
   By Graphics
   By Location
   Activity 3

7.  Exporting Maps
   Exporting
   Activity 4
  
 
FURTHER INFORMATION:
   General Information
   Data Sets

SELECTING DATA: BY LOCATION

Distance

ArcGIS can be used to find points of a given layer that occur within a specified distance from another layer using ‘Select by Location’ under the Selection menu. To find all public schools within 20 kilometres of a hospital complete the ‘Select by Location options as below.

Your map should now highlight all schools within 20 kilometres of a hospital.

A similar effect can be achieved by creating buffers around hospital points. Under the tools menu, choose ‘Buffer Wizard’. Choose to buffer the features of the layer hosp.txt and click Next. At the next screen, choose to create multiple rings (three, with a distance of 10 km between each ring). Then click Next.

At the next screen, you can choose whether or not you want the barriers of the buffers to dissolve when they overlap. Once you have chosen that, save the buffer as a new theme. When you click on Finish, a new theme will be created called Buffer of Hosp.txt. Pull the theme down so that it’s not covering the points.

To select all public schools within 30 kilometres of a hospital, first clear the previous selection. Go to Select by Location under the Selection menu. This time, choose to select features of the active theme that are completely within the selected features of your Buffer layer. When you click on New Set, all public schools that fall within your buffers will be highlighted.

Obviously, buffers are not necessary for determining distance from points, but they offer another option for doing it. Using another layer (a buffer in this case) for selecting data gives you many more options such as those listed below. This is especially important when selecting polygons or lines based on the features of another theme.

Activity 3. Selecting Data within WRHA

A. Determine the programs that are within 1 km of hospitals.

Add the program data (programs.dbf) table to the WRHA project. Using the postal code on the program file and the 1998 Winnipeg postal code locations (wpg_postal98), georeference each of the programs to a specific location using a join on postal code. You should realize that a number of programs do not have an associated postal code.

Join the Winnipeg CA areas to the program data so each program is identified with an individual community area. Change the symbol colours or shape to confirm that each program falls inside the appropriate community area. Identify all of the programs that fall within 1km of hospitals using the select by theme option. Save the selected programs into a new shape file.

B. Calculate distance from schools with Kindergarten classes to nearest hospital

Add the Winnipeg schools (wpg_public) to the WRHA view. Query (Select by Attributes) the schools attribute table to identify those with kindergarten classes (low_grade=’K’ or low_grade=’N’). Division 1 has some schools that start at nursery school (N) all of these schools also have kindergarten classes. You may also limit the data using the Definition property. Save this file as a projected shape file or the distance calculated in the join will be in the shape file units (decimal degrees – this is different than the spatial query above for some reason). Using the Join option for the new Kindergarten public schools do a spatial join with the hospital data. This will add a distance measurement for each school to the nearest hospital. In the attribute table query all kindergarten schools within 1 km of a hospital. Convert this to a shape file. Try to reverse the selection so you get all the schools more than 1 km from a hospital (hint: in the attribute table use the switch selection options menu item then select all of the kindergarten schools from that set).

You can do a similar selection using select by location options. An example is given below.


Introduction
Selecting Data: By Graphics
NEXT
Exporting Maps

 

Contact: Charles Burchill       Telephone: (204) 789-3429

Manitoba Centre for Health Policy
Department of Community Health Sciences, University of Manitoba
4th floor Brodie Centre
408 - 727 McDermot Avenue
Winnipeg, Manitoba R3E 3P5       Fax: (204) 789-3910
Last modified on Friday, 25-Aug-2006 08:06:00 CDT