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Clipping – ArcGIS 9

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Geospatial data often comes in geographies larger than what is required for a given project. For example, you may want only boundary files for a small area but your only choice may be to download boundary files for all of Canada. When you add other layers and clip their extent to your study area it reduces the amount of work for ArcGIS to do since any further analyses will be performed only on your clipped data.

This guide was show you two ways to extract features:

  • Selecting by attributes to create a subset.
  • Clip one layer based on the extent of another layer.

Data for the Guide

Our example will use DMTI Spatial Census tracts and Route Logistics roads files. The DRC site contains the DMTI Spatial files. Select Census Demographic Data & Boundaries > DMTI Census and CanMap Route Logistics Ver 2005.3.

Creating a Subset Based on Layer Attributes

In this task you will create a layer showing Guelph Census Tracts from a layer file of all Census Tracts for Canada.

  1. Open ArcMap and add the Canada census tract shape file.
  2. The program will ask if you want to open the program with a new, empty map, as a template or open an existing map project. When you are working with new data you will always open a new, empty map. Click the Add Data button, navigate to the location of the data file, select CANct.shp and click Add.

Select Guelph Census Tracts

  1. Open the Selection Menu > Select by Attributes.
  2. Build the expression ""PRCMA" = '35550' (35 is the ID code for Ontario and 550 is the ID code for Guelph, CA).
  3. Click Apply and close.
  4. From the Selection Menu > Zoom to selected features. Census tracts for Guelph are selected.

Create a New Shape File for Guelph Census Tracts

  1. Click on the Canada Census Tract layer in the Table of Contents and Select Data.
  2. Select Export Data. In the dialog box select the option, Export the selected features using the same coordinate system as the layer's source data. Name the file 550ct.shp.
  3. Display the new layer on the map and uncheck the visibility of your old layer. Now your map should have only Guelph Census Tracts.

Clip One Layer Based on the Extent of Another Layer

In this task you will add an Ontario roads file and clip its extent so that you have a new layer showing only the streets and roads for Guelph.

  1. Add the Guelph Census Tracts (550ct.shp) created above and the ONrte.shape file.
  2. Open ArcToolbox and expand the Analysis toolset and the Extract Tools by clicking on the + signs.
  3. Open the Clip tool by double-clicking on it.
  4. In the clip dialog box turn on Show help.
  5. In the Input Features use the drop down arrow to select Onrte.
  6. In the Clip Features use the drop down arrow to select 550ct.
  7. In the Output Feature class click the folder icon to navigate to your local directory. Save the clipped file as GUE_rte.shp.
  8. The new shape file is added to the view. Uncheck the visibility of the ONrte.

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Data Access

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519–824–4120 ext. 56417

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The DRC is located behind the Research Help desk in the McLaughlin Library.

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Last updated August 14th, 2007 by M.G. (details)