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How do you convert from USA Contiguous Albers Equal Area Conic to meters? Or, to latitude and longitude?

I am using ArcGIS 10.1, and within it, ArcMap. The shapefile I have reports the coordinates as USA Contiguous Albers Equal Area Conic. I want to take areas and distances of the polygons and they are very large due to the units. I am wondering how to convert to meters.

In particular, I want to do distance calculations, and I worry that Albers distorts the distances. How can get the most precise and meaningful distances when the shapefile orginated as Albers Equal Conic?

The shapefile is of United States counties. I would like to compute its distances within it.

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What software are you using? Do you want to convert a list of coordinates or actual geometry? – Fezter Oct 9 '12 at 5:21
Without knowing more about your problem, you may want to have a look at this site. It will help you convert between coordinate systems. – Fezter Oct 9 '12 at 5:31

1 Answer

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The coordinate system, USA Contiguous Albers equal area conic, by default is in meters, so any calculations you do should be in meters or square meters. Depending on how large the polygons are, the values could be very large. Did you want to have the values reported in kilometers instead? The Calculate Geometry tool lets you choose a different unit value.

In the ArcGIS for Desktop 10.1 help, the help topic is in Geodata, Data types, Tables, Calculating field values, Calculating area, length, and other geometric properties.

There's a small chance that someone modified the USA Contiguous Albers definition and changed the units. You can check this by looking at the coordinate system of the layer in ArcMap or ArcCatalog.

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How would I recover the latitude and longitude from these units? The distance I understand. Is this what you are saying to do in ArcMap or ArcCatalog? I am using ArcMap. What exactly would you suggest that I do? Is it by looking at the Attributes Table? That is where I discovered that the coordinates did not look like latitude or longitude for the United States!! – user1690130 Oct 9 '12 at 19:47
You can use Calculate Geometry to add the centroid or min or max coordinate values to an attribute table. One way is to open the attribute table in Arcmap. Set the data frame to use NAD 1983 (in geographic coord systems, N Amer) then you can choose for the coords to be in lat/lon. Or use the Project Tool to create a copy in the NAD 1983 system. – mkennedy Oct 9 '12 at 22:36
Thank you! Sorry, but how would one set the data frame to use NAD 1983? I've been looking at the Table of Contents part of the ArcMap screen, and I am not finding this option. – user1690130 Oct 9 '12 at 22:58
Also, is there a particular version of NAD 1983 that should be used? Googling around there seems to be a few. Like NAD 1983 (2011), NAD 1983 HARN, NAD 1983 (CSRS), NAD 1983, among others. – user1690130 Oct 9 '12 at 23:13
Right click Layers in the TOC or in the map itself and select Properties from the context menu. In the data frame properties dialog, select the coordinate systems tab. I would just use NAD 1983. – mkennedy Oct 9 '12 at 23:52
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