preserving-area projection for small area like Pakistan

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01-13-2022 08:49 AM
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lucky666
New Contributor

Dear all,

For my research on Pakistan settlements, I need to calculate the share of total settlement area in total area of Pakistan and the sum of length of settlement boundaries. For the former, as you suggested, it is important to use a projection preserving the areas. For the latter, I need to use a preserving-distance projection.

To have a projection that minimizes distortions to both areas and distance, I used the Israeli TM Grid projection tailored to my study area of Pakistan. Though this projection is only conformal, its focus on Pakistan helps minimize distortion of all properties in that region, according to the ArcGis website https://desktop.arcgis.com/en/arcmap/latest/map/projections/transverse-mercator.htm.

I wonder if this choice makes sense?

An alternative is to use transverse-cylindrical equal area projection for computing the share of settlement area mentioned above. But it targets the whole world rather than Pakistan. Also, I did not find equal-area projections targeting Pakistan. I am unsure whether I should prioritize having a projection targeting my study area (minimizing distortions of all local properties) over having a world-wide projection preserving areas. Could you please let me know if you have any suggestions?

(Similarly, I found a worldwide equal-distance projection for computing the lengths of settlement boundaries mentioned earlier.)

Thank you!

 

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DanPatterson
MVP Esteemed Contributor

UTM has a scale factor of 0.9996.  The Modified Transverse Mercator has one of 0.9999  (eg State Plane in the U.S, and MTM in Canada and elsewhere).   They are conformal the latter being "better" (bad term) since it uses a 3 degree lune rather than utm's 6 degree lune

For most purposes either of those should suit (perhaps less so at latitudes close to the poles).  If you are concerned about calculations resulting from the coordinate system, then do then with the geodesic options

Add Geometry Attributes (Data Management)—ArcGIS Pro | Documentation

for instance.

PS

fight the urge to rely on the projection to solve area/length "accuracy" issues, when not addressing the precision of the boundaries used to delineate the features themselves 😉


... sort of retired...

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DanPatterson
MVP Esteemed Contributor

UTM has a scale factor of 0.9996.  The Modified Transverse Mercator has one of 0.9999  (eg State Plane in the U.S, and MTM in Canada and elsewhere).   They are conformal the latter being "better" (bad term) since it uses a 3 degree lune rather than utm's 6 degree lune

For most purposes either of those should suit (perhaps less so at latitudes close to the poles).  If you are concerned about calculations resulting from the coordinate system, then do then with the geodesic options

Add Geometry Attributes (Data Management)—ArcGIS Pro | Documentation

for instance.

PS

fight the urge to rely on the projection to solve area/length "accuracy" issues, when not addressing the precision of the boundaries used to delineate the features themselves 😉


... sort of retired...
lucky666
New Contributor

Thank you very much for your very helpful information!

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