I want to resample a raster to a smaller cell size. The raster cell size is given in decimal degrees with a GCS of North America 1983. The original raster covers the continental US, and I have clipped it to a state level. I would like to be able to resample according to a 30 m cell size, with a projection for the state.

Should I use the Project raster tool? I only see information on the GCS, so I am not sure if there is a planar projected coordinate system. enter image description here


1 Answer 1


The Define Projection tool is used when assigning/defining a coordinate reference system (CRS) to a dataset that doesn't have one defined at all (or changing an incorrectly defined CRS). It doesn't change the underlying coordinates.

The Project Raster tool is used to transform a raster from one CRS to another. It does change the underlying coordinates.

Your data is in a Geographic CRS. So it has a correctly (I assume) defined CRS already. You don't want to assign a different CRS (Define Projection tool), if you did that your coordinates would not change but the coordinate system definition would and would then be incorrect.

You want to transform your raster to a different (projected) CRS using the Project Raster tool.

  • So if the Geographic CRS is the only existing system, does that mean there is not a current projected coordinate system? Or is the GCS NA 1983 acting as the geographic coordinate system and the projected coordinate system?
    – kent
    May 30, 2020 at 17:42
  • Yes, I think you're getting confused by Esri's use of the term "projection" to refer to both geographic and projected coordinate reference systems (and the term "project" to convert/transform between different CRSs, whether projected or geographic).
    – user2856
    May 31, 2020 at 0:04
  • I used project raster tool to convert GCS North America 1983 to California Albers Teale 1983 (projected coordinate system). Then I resampled the raster to a smaller cell size by specifying in meters. If I understand correctly, I am not changing the underlying datum because it remains NA 1983, I am just projecting to a planar coordinate system, in order to assess in meters. However, I am not sure at this point if the geographic coordinate system remains a part of the raster in some way, I don't see any reference to it in the properties tab.
    – kent
    May 31, 2020 at 1:28
  • A projected CRS is always based on a geographic CRS. desktop.arcgis.com/en/arcmap/10.3/GUIDE-BOOKS/MAP-PROJECTIONS/….
    – user2856
    May 31, 2020 at 2:32
  • Okay, this makes sense since a projected coordinate system is a projection of a geographic coordinate system. I wonder why I can't find reference to the GCS in the spatial properties tab in the layer properties. I assume it is in the background there as GCS North America 1983, but it would be useful to know how to identify it.
    – kent
    May 31, 2020 at 5:10

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