One of the most played maps (that I have seen) is the infamous Dual Gap. I thought I would take an hour or so to study the reclaim on the map. Attached to this post is an image which shows the regions I performed reclaim on.
Method
Reclaiming using UEF Sparky T2 Engineers (faster move speed than T1,2,3 engineers) for the area, then doing manual reclaim in areas to make sure the reclaim doesn't go out of the area being examined. Using the reclaim counter, then subtracting the previous area's reclaim to get the amount in the area being examined.
Overview
Each player is provided with 8 starting mex locations, and a hydro location. With 8 T1 mexes plus the ACU, each will be producing 17 mass per tick, so upgrading to T2 mexes shouldn't be a problem.
North
The North locations, including their rock areas, total about 11k Mass and 24k-27k Energy Reclaim each. Of this, 11k, 4k is in the rocks located in the orange squares. Meta for these locations is typically the top player doing an air build, with the bottom four players moving ACUs to the center for a land-based build.
South
The South locations, total around 5k Mass and 24k-26k Energy reclaim each. As with the top, the reclaim seems to be stacked toward the West Side. Meta for these locations is typically the bottom player doing air, and the top two players doing Naval builds.
Center
The center is, of course, the contested mass. 20k mass and 90k energy worth of reclaim to be had. Also, there are 5 Additional Mex locations in the north east and north west parts of the central area. There are 5 more in the south east and south west parts of the central area, along with 9 more central locations between them. There is also 9 more on an island just to the south. This is a feature exclusive to the V5.7 versions of this map.