From 25557cac1265916625e8d29f1b3473d6a7b88315 Mon Sep 17 00:00:00 2001
From: Tom MacWright <tom@macwright.org>
Date: Tue, 4 Dec 2012 18:13:23 -0500
Subject: [PATCH] Fine-tune zoom and center, make them properly match up with
 other maps

---
 js/id/renderer/background.js | 39 +++++++++++++++++++-----------------
 js/id/renderer/map.js        |  7 ++++---
 2 files changed, 25 insertions(+), 21 deletions(-)

diff --git a/js/id/renderer/background.js b/js/id/renderer/background.js
index 4032148ba..160f75424 100644
--- a/js/id/renderer/background.js
+++ b/js/id/renderer/background.js
@@ -62,22 +62,25 @@ iD.Background = function() {
 };
 
 // derive the url of a 'quadkey' style tile from a coordinate object
-iD.Background.Bing = function (coord) {
-    var template = 'http://ecn.t{t}.tiles.virtualearth.net/tiles/a{u}.jpeg?g=587&mkt=en-gb&n=z',
-        u = '';
-    for (var zoom = coord[2]; zoom > 0; zoom--) {
-        var byte = 0;
-        var mask = 1 << (zoom - 1);
-        if ((coord[0] & mask) !== 0) byte++;
-        if ((coord[1] & mask) !== 0) byte += 2;
-        u += byte.toString();
-    }
-    // distribute requests against multiple domains
-    var t = coord[2] % 5;
-    return template
-        .replace('{t}', t)
-        .replace('{u}', u)
-        .replace('{x}', coord[0])
-        .replace('{y}', coord[1])
-        .replace('{z}', coord[2]);
+iD.Background.template = function(template) {
+    return function(coord) {
+        var u = '';
+        for (var zoom = coord[2]; zoom > 0; zoom--) {
+            var byte = 0;
+            var mask = 1 << (zoom - 1);
+            if ((coord[0] & mask) !== 0) byte++;
+            if ((coord[1] & mask) !== 0) byte += 2;
+            u += byte.toString();
+        }
+        // distribute requests against multiple domains
+        var t = coord[2] % 5;
+        return template
+            .replace('{t}', t)
+            .replace('{u}', u)
+            .replace('{x}', coord[0])
+            .replace('{y}', coord[1])
+            .replace('{z}', coord[2]);
+    };
 };
+
+iD.Background.Bing = iD.Background.template('http://ecn.t{t}.tiles.virtualearth.net/tiles/a{u}.jpeg?g=587&mkt=en-gb&n=z');
diff --git a/js/id/renderer/map.js b/js/id/renderer/map.js
index 318129b4f..7638c98e6 100644
--- a/js/id/renderer/map.js
+++ b/js/id/renderer/map.js
@@ -444,9 +444,9 @@ iD.Map = function() {
 
     map.zoom = function(z) {
         if (!arguments.length) {
-            return Math.max(Math.log(projection.scale()) / Math.log(2) - 7, 0);
+            return Math.max(Math.log(projection.scale()) / Math.LN2 - 8, 0);
         }
-        var scale = 256 * Math.pow(2, z - 1),
+        var scale = 256 * Math.pow(2, z),
             center = pxCenter(),
             l = pointLocation(center);
         projection.scale(scale);
@@ -482,7 +482,8 @@ iD.Map = function() {
                 c = pxCenter(),
                 ll = projection(loc);
             projection.translate([
-                t[0] - ll[0] + c[0], t[1] - ll[1] + c[1]]);
+                t[0] - ll[0] + c[0],
+                t[1] - ll[1] + (c[1] /2)]);
             zoom.translate(projection.translate());
             return redraw();
         }