Javascript error: "Uncaught ReferenceError: map is not defined"

[WillySuMapSense]

In https://github.com/mapsense/polymaps-examples/blob/master/tile-browser.js, I found following code:

var map = po.map()
.container(mapDiv.append('svg')
....
var tj = po.d3TopoJson()
.url(url)
....
map.add(tj);

However, when I changed the variable name "var map" to something else such as "var map1":

var map1 = po.map()
.container(mapDiv.append('svg')
....
var tj = po.d3TopoJson()
.url(url)
....
map1.add(tj);

It gave me following error message in polymaps.js (lines 1586~1589):
"Uncaught ReferenceError: map is not defined"

    d3.select(g.insertBefore(po.svg("rect"), g.firstChild))
      .attr("width", map.tileSize().x)
      .attr("height", map.tileSize().x)
      .attr("class", "rectile");

I found out that "map" in "map.tileSize" is undefined and was used the global variable "map".

It seems to be the same case in lines 988~989

layer.map = function(x) {
if (!arguments.length) return map;

"map" in "return map" is using the global variable "map".

Expect:
Polymaps will work even we don't declare global variable "map".