# Building a raster in decimal degrees with areas in Sq.Km. as values

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07-24-2019 01:18 AM New Contributor II

I am trying to build a global raster at approx 500m resolution in geographic projection (cellsize 0.004167 decimal degrees), where values report the area of each cell in square meters.

I have built a Latitude grid that looks like this, where black is 0 and white is 90 and I applied the formula, which didn't work:

111113 * ((0.004167 * Cos("LatitudeRaster_500m" * 0.017453292)) * 0.004167)

Where 111113 is the length of 1 degree of arc at the equator; LatitudeRaster_500m is the latitude grid reporting the value of latitude of each cell and 0.004167 is the cellsize)

I realized that the problem is with the Cos("LatitudeRaster_500m") that, if run as such, generate a strange raster where the sequence of between -1  and 1 occurs several times like this (while = 1; black = -1) while I was expecting a raster with a 1 in the center, gradually moving to a 0 where the latitude is 90 degrees.

Any suggestion?

Many thanks

Fabio

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3 Replies by MVP Legendary Contributor New Contributor II

Thanks, but I don't want to project my raster layers. I have a pile of raster layers in geographic projection and would like to calculate areas using an additional raster with the area in Sq.Km of each cell as value.

Fabio New Contributor II

I solved the problem, the correct formula is:

(111319 * (0.004167 * Cos("Latitude_raster500" * 0.017453292)) * (0.004167 * 111319))

Where:

- 111319 is the length in meters of the arc of 1 degree at the Equator

- 0.004167 is the cell size in decimal degrees

- Latitude_raster500 is the raster layers of latitude values per cell

- 0.017453292 is the conversion factor from degrees to radiants (pi/180)

The output is a raster with the area of each cell as value

Best,

Fabio 