If you are seeing very small numbers for distance values, it’s likely due to a projection issue. See the instructions for Step 1. Your county polygon layer must be projected using a distance-preserving (equidistant) projection. If your polygon layer is instead in an unprojected Geographic Coordinate System with units expressed in decimal degrees, the results will also be in decimal degrees, an angular measurement. These angular measurements are of no use in calculating distance.

So be sure your polygon boundary file is projected before you begin step 1. See http://goo.gl/pMpb0 for an overview of projections and see http://goo.gl/oGkDG for help on the Project tool.

Thanks for the guide on using the Point Distance tool. I’m running into the same problem as Adam in New York. I’m calculating the distance between county centroids and place centroids, but I keep getting values in the 0.1 to 1.9 range.

Any tips?

Thanks,
Lena

This is great, but I’m still having trouble generating correct distance values. I’m calculating the distance between census tract centroids in New York State and I keep generating values in the range of 0.5-1.5. I have no idea what units these values are in; I am unable to find a conversion factor for miles that works consistently.

I have tried changing the projection of my centroid shape file but that has not helped.

Any advice would be much appreciated.

Thank you,
Adam

The ArcGIS tool “Generate Near Table” eliminates the centroid bias you describe. This tool assigns a “0″ distance to adjacent polygons. More info from the ArcGIS online help here: http://bit.ly/cZMD0d

Kelly Johnston