Dear all,
currently I am calculating surface area in ArcGIS (forests in Ethiopia) and am noticing the differences between the projections I am trying out. I am working with equal area projections (African Albert Equal Area Cone and Lambert Azimuthal Equal Area). Can someone recommend one of those or maybe a different one that is more accurate?
Kind regards,
Michele
Michèle von Kocemba try to use UTM (universal Transverse Mercator ) Projection. As Your study area is Ethiopia and its a Tropical country So UTM (https://gisgeography.com/utm-universal-transverse-mercator-projection/)will better for compute area.
Dear Michèle von Kocemba ,
The UTM projection system sometimes is not the best option for area calculation.
Measuring areas for a projection of the UTM system works very well within each zone, but when an area is between two or more zones (as in the example attached), there will inevitably be some kind of distortion (area, scale or shape), especially if you are further away from the zone.
Therefore, in these cases, it is better to choose a projection for your work that reduces area distortion. It can be cited: Albers Equal Area, Equal Area Cylindrical and Lambert Azimuthal Equal Area.
The Lambert Azimuthal Equal Area projection is most commonly used for measurements at the Earth's poles, so I suggest using Albers projection.
Using the Albers projection, you can set the projection parameters that make the surface of the cone best fit the surface of the Ethiopian region by reducing distortions. These parameters are: 1st standard parallel, 2nd standard parallel, Central Meridian, Latitude of projections origin, False Easting (meters), False Northing (meters).
Here are some links on the subject:
https://en.wikipedia.org/wiki/Lambert_azimuthal_equal-area_projection
https://en.wikipedia.org/wiki/Albers_projection
http://desktop.arcgis.com/en/arcmap/latest/map/projections/albers-equal-area-conic.htm
Now, if you really want to check the distortion for each projection in Ethiopia, I suggest you use the Matlab distortcalc function, described in the link below:
https://www.mathworks.com/help/map/ref/distortcalc.html
This study would be a good paper for congress!
http://www.geo.hunter.cuny.edu/~jochen/gtech201/lectures/lec6concepts/map%20coordinate%20systems/how%20to%20choose%20a%20projection.htm
these instructions could be helpful.
UTM (Universal Transverse Mercator) projection is best for calculating area which gives measurement in the form of SI unit like meter, kilometer, feet, etc. U try UTM projection with exact Zone Number.
Agreed, a projected, equidistant coordinate system is what you need and each country has a formal system for their region.
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