Finding the world center on blank SVG maps available on wikipedia

I need to plot geo locations (lat, lon) on svg maps just like it's done in this demo: http://people.opera.com/danield/svg/where-am-i.svg

I however have 3 blank maps not displaying the whole world. One of them is http://en.wikipedia.org/wiki/File:BlankMap-USA-states-Canada-provinces,_HI_closer.svg

There is seldom or no information about it on the web. I have been lo开发者_开发问答oking for a while but it seems like knowledge of the maps is required. I noticed the demo mentioned above first finds the world center, then multiply by a factor. How it's done is not really explained.

And as far as the world center, I wonder if I can find it on a map that's only displaying part of it.

Thanks a lot in advance for any help.

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The problem is that the coordinates used to build the SVG are not lat/long. Using the "world center" as (0,0) is a useful convention (place where the prime meridian meets the equator), but it will not allow for a very precise placement due to projection issues.

In your case, the line of latitude between Canada and the US combined with the longitude between Manitoba and Saskatchewan could be used as your "world center" (0,0) coordinate. Find out what the actual lat/long of that point is, then express other lat/long pairs relative to that one.

Again, I should restate that this is not a precise way of locating points, and there will be error especially when you get closer to the edges of the map.