diff --git a/mapgen.lua b/mapgen.lua
index 51cad83..6578c61 100644
--- a/mapgen.lua
+++ b/mapgen.lua
@@ -36,6 +36,12 @@ function init_mapgen()
       }
    }
 
+   -- Why is this hard-coded separately from the biome_data? glad you asked.
+   -- Lua's pairs() function appears not to guarantee a consistent return order,
+   -- and we want our world to be deterministically generated,
+   -- so the biome_metadata array needs to have its entries appear consistently.
+   biome_list = {"grassland", "forest", "desert"}
+
    init_biomes()
 end
 
@@ -43,13 +49,15 @@ function init_biomes()
    -- this is the frequency list for the biomes themselves
    biome_metadata = {}
 
-   for k,v in pairs(biome_data) do
+   for i=1,#biome_list do
+      local biome = biome_list[i]
+
       -- add the biome's name N times to the biome metadata 'hat'
-      for i=1,v["biome_frequency"] do
-         add(biome_metadata, k)
+      for i=1,biome_data[biome]["biome_frequency"] do
+         add(biome_metadata, biome)
       end
 
-      build_biome(k, v)
+      build_biome(biome, biome_data[biome])
    end
 end
 
@@ -76,10 +84,16 @@ function generate_uid(pos)
    return flr(rnd(-1))
 end
 
+-- given an {x,y} position, calculates the aligned starting position for the
+-- biome that position is in.
+function calculate_biome_pos(pos)
+   return {flr(pos[1] / biome_size), flr(pos[2] / biome_size)}
+end
+
 -- determines which biome a given world map position should be,
 -- returns the object out of the biome_data table
 function get_biome(pos)
-   local biome_pos = {flr(pos[1] / biome_size), flr(pos[2] / biome_size)}
+   local biome_pos = calculate_biome_pos(pos)
    local uid = generate_uid(biome_pos)
    local biome_name = biome_metadata[(uid % #biome_metadata) + 1]
    return biome_data[biome_name]