# Incorrect Polygon Area Calculations in ArcGIS Desktop?

I have converted a raster to a polygon, dissolved the polygons into singlepart, and tried to calculate areas using Calculate Geometry. Many of the areas are 'zero' or are areas that are obviously not correct.

How can I fix this?

When I calculate the areas for the undissolved polygons they appear to be correct. They are just subdivided into grid cells with the same spatial resolution as the Landsat image from which they are derived (30m x 30m). So, one grid cell has an area of 900 sq meters. The problem is that I need the grid cells dissolved so I can determine the exact number of polygons and their respective areas, hence the use of the dissolve tool.

The defined projection is WGS UTM Zone 9N (the same as the Landsat image) and it has never been changed.

• Try repair geometry resources.arcgis.com/en/help/main/10.2/index.html#//….. the area calculation fails on non-simple geometries which could be why you're having problems. If that doesn't help calculate the areas in the undissolved polygons then dissolve resources.arcgis.com/en/help/main/10.2/index.html#//… with a sum of area field. Nov 22, 2017 at 0:55
• Hi Michael, Thanks for your reply. Repair geometry does not seem to make a difference. I calculated areas for the undissolved polygons, then dissolved by the Area Field sum as you suggested, but it just assigns the sum of all of the areas to all of the polygons (so, they all have exactly the same area). Thoughts? Nov 22, 2017 at 1:23
• Did you specify your dissolve field so that not all polygons were made into one polygon? I'm assuming you have polygons with different values that you want to maintain but as an aggregate area of the same values. Nov 22, 2017 at 1:27
• I did not specify any dissolve field, just the Statistic Field with Area as the chosen field and Sum as the chosen statistic. This results in separate polygons (as desired), but all with the same value for Area (which is not correct). Nov 22, 2017 at 1:38
• Would it help for you to see the shapefiles? I can provide them. Nov 22, 2017 at 1:39