temperature affected by latitude, non-linearly

src/map_nextgen.lua

@@ -102,6 +102,11 @@ local generate = function()
         else
           temperature = temperature + altitude / 1000 -- -1 C / km (deep water adjustment)
         end
+        -- modify temperature by latitude
+        local polar_distance = math.abs(y - (map.size / 2))^1.1 -- experimenting with slight non-linearity
+        local max_temperature_delta = 40
+        temperature = temperature - (polar_distance / map.size * 2 * max_temperature_delta)
+        -- 'save' temperature changes
         map.temperature[x][y] = temperature
 
         -- choose biome