I have a question concerning area calculations in South-East Asia for West-East range that goes from India to Eastern Malaysia and a North-South range from Northern India to Indonesia (xMin,yMin 74.2203,-5.89636 : xMax,yMax 118.927,30.1183).
I found two projections that might be suitable for this geographical region:
- Albers Equal Area (Conical) for S-Asia (s. http://spatialreference.org/ref/esri/102028/)
and
- Pseudo/Web Mercator (EPSG:3857, s. http://spatialreference.org/ref/sr-org/7483/)
However, when I compare the results of both projections, I get large differences in total area (I used QGIS field calculator for area calculation):
- 620,589.41 km^2 for Albers Equal
and
- 689,941.23 km^2 for Pseudo Mercator
That is a difference of ard. 11%
Can anyone help me to understand the differences of these two projections and to know which one is more appropriate for my purpose?
Thanks so much in advance
Best Answer
Pseudo Mercator does not have real metres as units. At the equator it fits to metres but the more to the poles you come, the greater the distorsions are. The measurement tool takes care of that, but the field calculator does not.
So you have to choose another CRS. Most UTM CRS are restricted to their defined area, and might produce wrong results outside.