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Defining a raster's coordinate system
Release 9.2
Last modified September 22, 2008		 E-mail This Topic Printable Version Give Us Feedback

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About defining a raster's coordinate system

The Spatial Reference section on the Raster Dataset Properties dialog box shows the raster dataset’s map projection and lists parameters of the projection. The projection defines how coordinates describing locations on the earth’s surface are mathematically transformed to accurately represent them on a flat map sheet with the least amount of distortion. There will always be some sort of distortion in geographic data, since you are trying to put three-dimensional data onto a two-dimensional plane. When you choose a spatial reference, you need to choose the projection that will minimize the type of distortion you are most concerned about.

If the raster dataset doesn’t have a coordinate system, you can assign one by clicking the Edit button. The Edit button will also display more details about the existing coordinate system if one is already defined. If the raster dataset is a grid, you will see the Define Projection Wizard. You can either define the coordinate system’s parameters interactively or copy the information from another coverage, grid, or TIN.
If the raster dataset already has coordinate system information, you can also use the Define Projection Wizard to change that information. If the raster dataset exists as a format other than a grid, you will see the Spatial Reference Properties dialog box. Converting from one projection to another can also change the shape and area a cell represents on the surface of the earth. Each projection treats the relationship between a three-dimensional world and a two-dimensional one differently. You should be aware of the properties and assumptions for each projection before selecting one.

Learn more about map projections


How to define a raster's coordinate system

Defining or modifying a raster's (nongrid) coordinate system

  1. Click the raster whose coordinate system you want to define.
  2. Click the File menu and click Properties.
  3. Scroll down to the Spatial Reference section.
  4. Click Edit.
  5. On the Spatial Reference Properties dialog box, click Select and choose a predefined coordinate system. Browse the coordinate system folder, click the one that is required for your raster dataset, then click Add. You may need to open several folders before you can choose your correct projection.
    6. Or click Import and choose the data source whose coordinate system parameters you want to copy.
    Or click New, click Geographic or Projected, then define a new, custom coordinate system. Each of these options is described in detail in Defining a shapefile's coordinate system.

  6. Click OK on the Spatial Reference dialog box.
  7. Click OK on the Raster Dataset Properties dialog box.


Defining a grid's coordinate system interactively

  1. Click the grid whose coordinate system you want to define.
  2. Click the File menu and click Properties.
  3. Scroll down to the Spatial Reference section.
  4. Click Edit.
  5. Make sure the Define the coordinate system interactively option is selected.
  6. Click Next.
  7. Click the appropriate coordinate system in the Projections list on the left.

    8. A description of the coordinate system appears on the right.
  8. Click Next.
  9. Type the appropriate parameter values for the coordinate system; each has a different set of parameters.
  10. Click Next.
  11. If the grid uses a projected coordinate system, click the datum it uses or click Spheroid and define the spheroid's parameters.
  12. Click Next.
  13. Review the summary of the coordinate system that will be assigned to the grid. If you want to change an entry, go back through the wizard by clicking the Back button.
  14. Click Finish if you want to use this coordinate system.
  15. Click OK on the Raster Dataset Properties dialog box.

Tips

  • If you want to change any of the parameters in the wizard, you can go back by clicking the Back button.

  • The way you define the coordinate system of a raster dataset that is a grid is the same way you would define a coordinate system for a coverage or a TIN.

Matching another dataset's coordinate system to a grid

  1. Click the grid whose coordinate system you want to define.
  2. Click the File menu and click Properties.
  3. Scroll to the Spatial Reference section and click Edit.
  4. Click the Define a coordinate system for my data to match existing data option.
  5. Click Next.
  6. Click the Dataset Browse button Browse button.
  7. Navigate to and click the dataset whose coordinate system you want to use.
  8. Click Open.
  9. Review the coordinate system's parameters that appear in the wizard. If you want to use this coordinate system, click Next. Otherwise, click Back and locate a different coverage.
  10. Click Finish.

    11. The coordinate system and its parameters appear on the dataset's Properties dialog box.
  11. Click OK.

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