diff --git a/generate.lua b/generate.lua
index 3025e26..ddfdb3e 100644
--- a/generate.lua
+++ b/generate.lua
@@ -1,7 +1,6 @@
 local EvolutionModel = dofile(mapgen_rivers.modpath .. '/terrainlib_lua/erosion.lua')
 local twist = dofile(mapgen_rivers.modpath .. '/terrainlib_lua/twist.lua')
 
-local size = {x=1000, y=1000}
 local blocksize = 12
 local variation_speed = 70
 
@@ -21,6 +20,9 @@ local niter = math.ceil(time/time_step)
 time_step = time / niter
 
 local function generate()
+	local grid = mapgen_rivers.grid
+	local size = grid.size
+
 	local seed = tonumber(minetest.get_mapgen_setting("seed"))
 	np_base.seed = (np_base.seed or 0) + seed
 
@@ -65,6 +67,13 @@ local function generate()
 	local sfile = io.open(mapgen_rivers.world_data_path .. 'size', "w")
 	sfile:write(size.x..'\n'..size.y)
 	sfile:close()
+
+    grid.dem = model.dem
+    grid.lakes = model.lakes
+    grid.dirs = model.dirs
+    grid.rivers = model.rivers
+    grid.offset_x = offset_x
+    grid.offset_y = offset_y
 end
 
 return generate
diff --git a/load.lua b/load.lua
index 740e3f8..f7ad294 100644
--- a/load.lua
+++ b/load.lua
@@ -42,6 +42,7 @@ function mapgen_rivers.write_map(filename, data, bytes)
 
     for i=1, size do
         local n = mfloor(data[i])
+        data[i] = n
         for j=bytes, 2, -1 do
             bytelist[j] = n % 256
             n = mfloor(n / 256)
diff --git a/polygons.lua b/polygons.lua
index d767b26..1459b45 100644
--- a/polygons.lua
+++ b/polygons.lua
@@ -9,36 +9,41 @@ minetest.mkdir(world_data_path)
 
 dofile(modpath .. 'load.lua')
 
+mapgen_rivers.grid = {}
+
+local X = 1000
+local Z = 1000
+
 -- Try to read file 'size'
 local sfile = io.open(world_data_path..'size', 'r')
-if not sfile then
+if sfile then
+	X, Z = tonumber(sfile:read('*l')), tonumber(sfile:read('*l'))
+	sfile:close()
+	minetest.register_on_mods_loaded(function()
+		local grid = mapgen_rivers.grid
+		grid.dem = mapgen_rivers.load_map('dem', 2, true, X*Z)
+		grid.lakes = mapgen_rivers.load_map('lakes', 2, true, X*Z)
+		grid.dirs = mapgen_rivers.load_map('dirs', 1, false, X*Z)
+		grid.rivers = mapgen_rivers.load_map('rivers', 4, false, X*Z)
+
+		grid.offset_x = mapgen_rivers.load_map('offset_x', 1, true, X*Z)
+		grid.offset_y = mapgen_rivers.load_map('offset_y', 1, true, X*Z)
+	end)
+else
 	-- Generate a map!!
 	local generate = dofile(mapgen_rivers.modpath .. '/generate.lua')
-	generate()
-	sfile = io.open(world_data_path..'size', 'r')
+	minetest.register_on_mods_loaded(generate)
 end
 
--- Read the map
--- TODO: if data has just been generated, transfer it without reloading everything
-local X = tonumber(sfile:read('*l'))
-local Z = tonumber(sfile:read('*l'))
-sfile:close()
+minetest.register_on_mods_loaded(function()
+	local offset_x, offset_y = mapgen_rivers.grid.offset_x, mapgen_rivers.grid.offset_y
+	for i=1, #offset_x do
+		offset_x[i] = (offset_x[i]+0.5) * (1/256)
+		offset_y[i] = (offset_y[i]+0.5) * (1/256)
+	end
+end)
 
-local dem = mapgen_rivers.load_map('dem', 2, true, X*Z)
-local lakes = mapgen_rivers.load_map('lakes', 2, true, X*Z)
-local dirs = mapgen_rivers.load_map('dirs', 1, false, X*Z)
-local rivers = mapgen_rivers.load_map('rivers', 4, false, X*Z)
-
-local offset_x = mapgen_rivers.load_map('offset_x', 1, true, X*Z)
-for k, v in ipairs(offset_x) do
-	offset_x[k] = (v+0.5)/256
-end
-
-local offset_z = mapgen_rivers.load_map('offset_y', 1, true, X*Z)
-for k, v in ipairs(offset_z) do
-	offset_z[k] = (v+0.5)/256
-end
--- Should have finished loading
+mapgen_rivers.grid.size = {x=X, y=Z}
 
 local function index(x, z)
 	return z*X+x+1
@@ -86,6 +91,15 @@ local function make_polygons(minp, maxp)
 	print("Generating polygon map")
 	print(minp.x, maxp.x, minp.z, maxp.z)
 
+	local grid = mapgen_rivers.grid
+	local dem = grid.dem
+	local lakes = grid.lakes
+	local dirs = grid.dirs
+	local rivers = grid.rivers
+
+	local offset_x = grid.offset_x
+	local offset_z = grid.offset_y
+
 	if not init then
 		if glaciers then
 			noise_heat = minetest.get_perlin(mapgen_rivers.noise_params.heat)