geolocation sets zoom based on accuracy

fixes #1375

js/id/geo.js

@@ -85,7 +85,3 @@ iD.geo.pathLength = function(path) {
     }
     return length;
 };
-
-iD.geo.metersToCoordinates = function(loc, vector) {
-    return [vector[1] / 111200, vector[0] / 111200 / Math.abs(Math.cos(loc[1]))];
-};

js/id/geo/extent.js

@@ -33,5 +33,13 @@ _.extend(iD.geo.Extent.prototype, {
                obj[0][1] <= this[1][1] &&
                obj[1][0] >= this[0][0] &&
                obj[1][1] >= this[0][1];
+    },
+
+    padByMeters: function(meters) {
+        var dLat = meters / 111200,
+            dLon = meters / 111200 / Math.abs(Math.cos(this.center()[1]));
+        return iD.geo.Extent(
+                [this[0][0] - dLon, this[0][1] - dLat],
+                [this[1][0] + dLon, this[1][1] + dLat]);
     }
 });

js/id/ui/geolocate.js

@@ -5,7 +5,10 @@ iD.ui.Geolocate = function(map) {
     }
 
     function success(position) {
-        map.center([position.coords.longitude, position.coords.latitude]);
+        var extent = iD.geo.Extent([position.coords.longitude, position.coords.latitude])
+            .padByMeters(position.coords.accuracy);
+
+        map.centerZoom(extent.center(), Math.min(20, map.extentZoom(extent)));
     }
 
     function error() { }

js/id/ui/preset/address.js

@@ -12,10 +12,7 @@ iD.ui.preset.address = function(field, context) {
 
         var extent = entity.extent(context.graph()),
             l = extent.center(),
-            dist = iD.geo.metersToCoordinates(l, [200, 200]),
-            box = iD.geo.Extent(
-                    [extent[0][0] - dist[0], extent[0][1] - dist[1]],
-                    [extent[1][0] + dist[0], extent[1][1] + dist[1]]);
+            box = iD.geo.Extent(l).padByMeters(200);
 
         return context.intersects(box)
             .filter(isAddressable)