diff --git a/src/mw_engine/utils.clj b/src/mw_engine/utils.clj
index dc81b52..33b63bc 100644
--- a/src/mw_engine/utils.clj
+++ b/src/mw_engine/utils.clj
@@ -124,3 +124,30 @@
     (get-neighbours-with-state world (:x cell) (:y cell) depth state))
   ([world cell state]
     (get-neighbours-with-state world cell 1 state)))
+
+(defn- set-cell-property
+  "If this `cell`s x and y properties are equal to these `x` and `y` values,
+   return a cell like this cell but with the value of this `property` set to
+   this `value`. Otherwise, just return this `cell`."
+  [cell x y property value]
+  (cond 
+    (and (= x (:x cell)) (= y (:y cell)))
+    (merge cell {property value})
+    true
+    cell))
+
+(defn set-property
+  "Return a world like this `world` but with the value of exactly one `property`
+   of one `cell` changed to this `value`"
+  ([world cell property value]
+    (set-property world (:x cell) (:y cell) property value))
+  ([world x y property value]
+    (apply 
+      vector ;; we want a vector of vectors, not a list of lists, for efficiency
+      (map
+        (fn [row]
+          (apply
+            vector
+            (map #(set-cell-property % x y property value)
+                 row)))
+        world))))
diff --git a/test/mw_engine/utils_test.clj b/test/mw_engine/utils_test.clj
index 09708f9..b6dfd0f 100644
--- a/test/mw_engine/utils_test.clj
+++ b/test/mw_engine/utils_test.clj
@@ -1,6 +1,7 @@
 (ns mw-engine.utils-test
   (:use [mw-engine.world :as world])
   (:require [clojure.test :refer :all]
+            [clojure.math.combinatorics :as combo]
             [mw-engine.utils :refer :all]))
 
 (deftest get-neighbours-test
@@ -101,3 +102,45 @@
                  (is (= (get-neighbours-with-property-value world 3 3 1 :deer 2)
                         '({:altitude 72, :x 3, :y 2, :deer 2} 
                            {:altitude 100, :x 3, :y 4, :deer 2}))))))
+
+(deftest set-property-test
+  (testing "The set-property utility function"
+           (let [w1a (make-world 3 3)
+                 w2b (set-property w1a (get-cell w1a 1 1) :location :centre)
+                 w3c (set-property w2b 0 0 :location :top-left)]
+             (is (= (:location (get-cell w3c 0 0) :top-left)))
+             (is (= (:location (get-cell w3c 1 1) :centre)))
+             (is (nil? (:location (get-cell w3c 2 2))) 
+                 "Cell at 2,2 should not have location set")
+             (is (= (count (remove nil? (map #(:location %) (flatten w3c)))) 2)
+                 "Third world should have two location properties set")
+             (is (= (count (remove nil? (map #(:location %) (flatten w2b)))) 1)
+                 "Second world should have only one location set")
+             (is (zero? (count (remove nil? (map #(:location %) (flatten w1a)))))
+                 "First world should not have any location properties set")
+             (is 
+               (empty?
+                 (remove 
+                   true? 
+                   (map #(= (:x (get-cell w3c (nth % 0) (nth % 1))) (nth % 0))
+                        (combo/cartesian-product (range 0 3)
+                                                 (range 0 3)))))
+               "No X coordinates were injured in the production of this world")
+             (is 
+               (empty?
+                 (remove 
+                   true? 
+                   (map #(= (:y (get-cell w3c (nth % 0) (nth % 1))) (nth % 1)) 
+                        (combo/cartesian-product (range 0 3)
+                                                 (range 0 3)))))
+               "No Y coordinates were injured in the production of this world")
+             (is 
+               (empty?
+                 (remove 
+                   false? 
+                   (map #(= (:y (get-cell w3c (nth % 0) (nth % 1))) 1234567) 
+                        (combo/cartesian-product (range 0 3)
+                                                 (range 0 3)))))
+               "General sanity test")
+             )))
+            
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