The first two arguments to strpaste() are the string to place on the left, and string to place on the right. I reversed these, and the result seems to be what you intend.
Code:
if(worldmap)
send_to_char(ch, "%s", strpaste(WorldMap(centre, size, MAP_CIRCLE, MAP_COMPACT), strfrmt(str, GET_SCREEN_WIDTH(ch) - char_size, size*2 + 1, FALSE, TRUE, TRUE), " \tn"));
else
send_to_char(ch, "%s", strpaste(CompactStringMap(centre, size), strfrmt(str, GET_SCREEN_WIDTH(ch) - char_size, size*2 + 1, FALSE, TRUE, TRUE), " \tn"));
