Calculating area per range of values (classes) in raster using ArcGIS?

Question

My data consists of several points each with xy coordinates and height.

I used spatial analyst tools -> interpolation -> natural neighbor to get an interpolation map for the height distribution, separated in categories like 10m-20m, 20m-30m and so on. This works fine.

Now, I would like to get the area of those categories. For example, I want to see that the interpolated area in the 10m-20m range is 200m².

Answer 1

When calculating areas, be aware in which Coordinate Reference System (CRS) data is defined and pay attention if used tools are honoring the CRS (as opposed to project data on the fly and then, calculate areas).

Also, verify if the calculation method is aligned with your goal. For example, a projected coordinate system will yield planar areas (the area in a cartesian system), and if it is an equal area projection the result will be exact, otherwise, approximate. A geographic coordinate system will yield geodetic areas (the area based on a geoid/ellipsoid).

First, get the height classes from the raster resulted from the interpolation analysis:

• Use the Reclassify tool to convert continuous values of height into desired classes (bins): 10m-20m, 20m-30m, etc. Set the remap parameter equal to RemapRange, i.e., each value within a given range (class) will be remapped to a common value.

From here, there are two main strategies:

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1. Calculate areas directly from the raster;

If CRS is in a projected coordinate system, one can count how many pixels exist in each class and multiply them by the pixel area. See Measuring area of raster classes?.

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2. Convert the Raster to Polygon and then, calculate areas (for each polygon):

There are several tools (some of them use different methods) one can use to calculate area from polygons:

• Field Calculator. Supports both planar and geodetic areas.

See the following example from Mahr (2015) - Calculating Geodesic Areas in ArcMap with Field Calculator:

!Shape!.getArea("GEODESIC","SQUAREKILOMETERS")

• Calculate Geometry. Supports only planar area (i.e., if CRS is projected);
• Add Geometry Attributes. Support both planar and geodetic areas.
• Calculate Areas (use it only if CRS is projected);

After calculating areas from polygons, add up (sum) their areas within each height class using the Summary Statistics tool.