--- a/src/road_cmd.cpp	Wed Jan 16 01:27:24 2008 +0000
+++ b/src/road_cmd.cpp	Wed Jan 16 02:53:55 2008 +0000
@@ -1203,14 +1203,14 @@
 
 	const Town* t = ClosestTownFromTile(tile, (uint)-1);
 	if (!HasRoadWorks(tile)) {
-		int grp = 0;
+		HouseZonesBits grp = HZB_TOWN_EDGE;
 
 		if (t != NULL) {
 			grp = GetTownRadiusGroup(t, tile);
 
 			/* Show an animation to indicate road work */
 			if (t->road_build_months != 0 &&
-					(DistanceManhattan(t->xy, tile) < 8 || grp != 0) &&
+					(DistanceManhattan(t->xy, tile) < 8 || grp != HZB_TOWN_EDGE) &&
 					GetRoadTileType(tile) == ROAD_TILE_NORMAL && CountBits(GetAllRoadBits(tile)) > 1 ) {
 				if (GetTileSlope(tile, NULL) == SLOPE_FLAT && EnsureNoVehicleOnGround(tile) && Chance16(1, 40)) {
 					StartRoadWorks(tile);

--- a/src/town.h	Wed Jan 16 01:27:24 2008 +0000
+++ b/src/town.h	Wed Jan 16 02:53:55 2008 +0000
@@ -44,13 +44,21 @@
 
 DECLARE_ENUM_AS_BIT_SET(BuildingFlags)
 
+enum HouseZonesBits {
+	HZB_TOWN_EDGE = 0,
+	HZB_TOWN_OUTSKIRT,
+	HZB_TOWN_OUTER_SUBURB,
+	HZB_TOWN_INNER_SUBURB,
+	HZB_TOWN_CENTRE,
+};
+
 enum HouseZones {                  ///< Bit  Value       Meaning
 	HZ_NOZNS             = 0x0000,  ///<       0          This is just to get rid of zeros, meaning none
-	HZ_ZON1              = 0x0001,  ///< 0..4 1,2,4,8,10  which town zones the building can be built in, Zone1 been the further suburb
-	HZ_ZON2              = 0x0002,
-	HZ_ZON3              = 0x0004,
-	HZ_ZON4              = 0x0008,
-	HZ_ZON5              = 0x0010,  ///<                  center of town
+	HZ_ZON1              = 1U << HZB_TOWN_EDGE,    ///< 0..4 1,2,4,8,10  which town zones the building can be built in, Zone1 been the further suburb
+	HZ_ZON2              = 1U << HZB_TOWN_OUTSKIRT,
+	HZ_ZON3              = 1U << HZB_TOWN_OUTER_SUBURB,
+	HZ_ZON4              = 1U << HZB_TOWN_INNER_SUBURB,
+	HZ_ZON5              = 1U << HZB_TOWN_CENTRE,  ///<  center of town
 	HZ_ZONALL            = 0x001F,  ///<       1F         This is just to englobe all above types at once
 	HZ_SUBARTC_ABOVE     = 0x0800,  ///< 11    800        can appear in sub-arctic climate above the snow line
 	HZ_TEMP              = 0x1000,  ///< 12   1000        can appear in temperate climate
@@ -315,7 +323,7 @@
 bool CheckIfAuthorityAllows(TileIndex tile);
 Town *ClosestTownFromTile(TileIndex tile, uint threshold);
 void ChangeTownRating(Town *t, int add, int max);
-uint GetTownRadiusGroup(const Town* t, TileIndex tile);
+HouseZonesBits GetTownRadiusGroup(const Town* t, TileIndex tile);
 void SetTownRatingTestMode(bool mode);
 
 #endif /* TOWN_H */

--- a/src/town_cmd.cpp	Wed Jan 16 01:27:24 2008 +0000
+++ b/src/town_cmd.cpp	Wed Jan 16 02:53:55 2008 +0000
@@ -1622,18 +1622,22 @@
 	return CmdSucceeded(DoCommand(tile, 0, 0, DC_EXEC | DC_AUTO | DC_NO_WATER, CMD_LANDSCAPE_CLEAR));
 }
 
-
-uint GetTownRadiusGroup(const Town* t, TileIndex tile)
+/** Returns the bit corresponding to the town zone of the specified tile
+ * @param t Town on which radius is to be found
+ * @param tile TileIndex where radius needs to be found
+ * @return the bit position of the given zone, as defined in HouseZones
+ */
+HouseZonesBits GetTownRadiusGroup(const Town* t, TileIndex tile)
 {
 	uint dist = DistanceSquare(tile, t->xy);
-	uint smallest;
+	HouseZonesBits smallest;
 	uint i;
 
-	if (t->fund_buildings_months && dist <= 25) return 4;
-
-	smallest = 0;
+	if (t->fund_buildings_months && dist <= 25) return HZB_TOWN_CENTRE;
+
+	smallest = HZB_TOWN_EDGE;
 	for (i = 0; i != lengthof(t->radius); i++) {
-		if (dist < t->radius[i]) smallest = i;
+		if (dist < t->radius[i]) smallest = (HouseZonesBits)i;
 	}
 
 	return smallest;
@@ -1677,9 +1681,10 @@
 	/* Above snow? */
 	slope = GetTileSlope(tile, &z);
 
-	/* Get the town zone type */
+	/* Get the town zone type of the current tile, as well as the climate.
+	 * This will allow to easily compare with the specs of the new house to build */
 	{
-		uint rad = GetTownRadiusGroup(t, tile);
+		HouseZonesBits rad = GetTownRadiusGroup(t, tile);
 
 		int land = _opt.landscape;
 		if (land == LT_ARCTIC && z >= _opt.snow_line) land = -1;
@@ -1699,6 +1704,7 @@
 		/* Generate a list of all possible houses that can be built. */
 		for (i = 0; i < HOUSE_MAX; i++) {
 			hs = GetHouseSpecs(i);
+			/* Verify that the candidate house spec matches the current tile status */
 			if ((~hs->building_availability & bitmask) == 0 && hs->enabled) {
 				if (_loaded_newgrf_features.has_newhouses) {
 					probability_max += hs->probability;