# Which projection is suitable for the measurements of this great circle?

I have drawn a circle on google earth pro in such a way that its radius starts from earth center 0,0 (lat/long) and ends at 0,90 (lat/long). This circle divide the earth into two equall halfs as shown in image. It is in line shape of length 39,999 km.

Then I have converted this circle in ArcGIS format and visualize there, it seem to be in a rectangle shape, obviously due to projection . When I select web mercator or other projected coordinate system of world they all give too much length as compared to its actual length 39,999 km.

My questions are:

1. What method or suitable projection should I adopt in order to calculate its length on ArcMap?
2. Length of this circle on google earth is 39,999 km which is different from the earth circumference which is about 40,075 km, why?
• in this direction, it should be an ellipse, not a circle, because the Earth is flattened. It is approximatively 40008 km Commented Aug 28, 2015 at 12:02
• In ArcGIS as a complete line, I can only think of Stereographic, which displays half the world, centered on 0,0 (or anywhere on the equator), but then you'd have to measure the perimeter somehow...using a geodesic method. Or transverse Mercator, other cylindrical projections and treat it as two lines. Commented Aug 28, 2015 at 16:06
• I have tried this method but this give too much length, but when I use measure tool for this rectangle shape on WGS 1984 projection it give a result of around 40,000 km which is acceptable. Commented Aug 29, 2015 at 5:55