# Choosing Equal Area Projection and Standard Parallels for Indonesia?

I am trying to do area computation stuff over whole of Indonesia and as such, am using the following projection:

http://spatialreference.org/ref/esri/asia-south-albers-equal-area-conic/

To make this projection work over Indonesia, I am following the guidelines give at the following link:

The recommended modifications change the following:

central meridian: 115.0 (from 125)

standard parallel 1: 2.0 (from 7)

standard parallel 2: -7.0 (from -32)

latitude of origin: 0.0 (from -15)

I think central meridian and latitude of origin do not impact distortions in any manner. However, why is it that the standard parallels should be 2 and -7? The entirety of Indonesia does not seem to be lying within these latitudes. From my inspection of the map, the entirety of Indonesia would lie somewhere between 6 and -11. Wouldn't these be better choices? How does a change of standard parallels/secants impact the computations?

• The standard parallels are where "true scale" lies, and to the north and south distortion increases. Putting them nearer to the centre means that more of the central region is "optimal". Also, see this for conic discussoin generally en.wikisource.org/wiki/The_American_Practical_Navigator/… Jun 14, 2015 at 22:20
• @mdsumner What do you mean by putting them to the center? Does center in my case represent whole of Indonesia, and I should put entire Indonesia b/w my standard parallels? If that is so, would 6 and -11 be better choices than 2 and -7? Jun 14, 2015 at 23:17
• Data between the 2 std parallels have to be squashed to fit onto the conic surface. Data above the upper std parallel and below the lower std parallel have to be stretched to fit onto the surface. Choosing std parallels somewhere within the area of interest reduces the overall distortion. Jun 15, 2015 at 17:49