Began fixing bugs with caused by asynchronous listener calls.

#bug

src/main/java/seng302/visualiser/map/Boundary.java

@@ -0,0 +1,44 @@
+package seng302.visualiser.map;
+
+/**
+ * The Boundary class represents a rectangle territorial boundary on a map. It
+ * contains four extremity double values(N, E, S, W). N and S are represented as
+ * latitudes in radians. E and W are represented as longitudes in radians.
+ *
+ * Created by Haoming on 10/5/17
+ */
+class Boundary {
+
+	private double northLat, eastLng, southLat, westLng;
+
+	Boundary(double northLat, double eastLng, double southLat, double westLng) {
+		this.northLat = northLat;
+		this.eastLng = eastLng;
+		this.southLat = southLat;
+		this.westLng = westLng;
+	}
+
+	double getCentreLat() {
+		return (northLat + southLat) / 2;
+	}
+
+	double getCentreLng() {
+		return (eastLng + westLng) / 2;
+	}
+
+	double getNorthLat() {
+		return northLat;
+	}
+
+	double getEastLng() {
+		return eastLng;
+	}
+
+	double getSouthLat() {
+		return southLat;
+	}
+
+	double getWestLng() {
+		return westLng;
+	}
+}