Projecting coverages or grids in ARC/INFO

There are three or four common projections used for Wyoming datasets, and literally hundreds used through the U.S. and the world. What projection your dataset is in depends on where you got it, what area it covers, and its source (the original map or database it was derived from). If you are not sure what projection your coverage or grid is in, use the DESCRIBE command:

Arc: describe -coverage name-

Or, if your data has a metadata document associated with it, look under the Spatial Reference Information section.

Here is an example of the PROJECT command in ARC/INFO:

Arc: project cover roadslam roadsutm lam-utm12

This is a coverages of roads in lambert projection, that is being changed to UTM zone 12. "lam-utm12" is the name of a text file that contains the projection parameters.

Here is another example of the PROJECT command for a grid, changing from UTM zone 12 to zone 13:

Arc: project grid dem12 dem13 utm12-utm13

One thing you need to be careful about when performing projections is that you check what datum that your data is in. For instance, the North American Datum of 1927 (NAD27) is still commonly used, though there is a more recent datum from 1983 (NAD83), in which most USGS and many clearinghouse datasets are made available in. GPS data will sometimes be in WGS84 datum. For more about datums, look at several projection files provided below.

Here are several examples of projection files that you can use (use SAVE AS text format to download)

  • From UTM 12 to UTM 13, same datum: utm12-utm13
  • From UTM 12 NAD27 to decimal degrees, NAD83: utm12-dd83
  • From Lambert Conformal Conic (a statewide projection) to UTM zone 13: lam-utm13
  • From decimal degrees to Albers (a nationwide projection) dd-alb

Can you project a shapefile in ARC/INFO?

No, but you can convert a shapefile to a coverage and then project it. The first parameter of the SHAPEARC command is the shapefile's name, then the new name for the coverage.

  • Example for a point shapefile: shapearc city citycov
  • Example for a line shapefile: shapearc streams streamcov
    If your line shapefile is a network route, then specify a name for the subclass parameter in order to create a RAT table
  • Example for a polygon shapefile: shapearc soils soilreg type

This creates an additional INFO table called soilreg.pattype, from the subclass "type". Shape polygon features are converted into REGIONS because there is no way to insure that polygon shape features do not overlap. If polygon topology is required the REGIONPOLY command can be used, for instance: regionpoly soilreg soilcov type. The attribute information stored in the subclass table "type" is then joined to the PAT table of the new coverage soilcov, which is a true polygon coverage, no longer a region coverage.