[GRASS-user] Add up several maps, which hold different regions, with mapcalc

[Büro Seling]

Dear Group,

I could not find a way to add up several maps, which hold different 
regions, with mapcalc.

Within a larger GRASS location (i.e. 80x80 km) I have to make several 
viewshed/line-of-sight analyses.
Each one with a radius of 5000 meters.
In the end,with mapcalc, I have to add up all these single maps into one 
map which then contains the information in which place how many items 
can be seen.
So fare no problem.
Then I had the idea to spare time and do the viewshed/line-of-sight 
analyses within a smaller region (5000x5000m, just the area I need for 
the single calcuations).
Also up to now no Problem.
My problem begins, when I now try to add up all these single maps into 
one larger map.
I searched for a solution and tried several things, but nothing worked.

Any tipps or hinds?

Thx
Stefan