How to Automatically Create ImageMaps of Grey Maps from Wikipedia?

Question

I have a project using various members of Wikipedia's grey maps: http://en.wikipedia.org/wiki/Wikipedia:Blank_maps. I fill them in with colors depending on which countries, states or provinces a user selects by clicking on the shape or by checking a checkbox.

I would like to write a script that creates imagemaps automatically of each country, state or province by somehow getting the X and Y pixel location of the borders of a country, state or province albeit without the names of these entities, which I will fill in later. I have already done the World map by hand and found a open source US map image map demo. I would now like to create my maps more rapidly.

I use PHP and GD to floodfill the shapes, so I guess I could use one central pixel location of the shapes as well. Any suggestions? This script is a possibility but is still somewhat manual: http://abhinavsingh.com/blog/2009/03/using-image-maps-in-javascript-a-demo-application/. Also Mapedit, http://www.boutell.com/mapedit/, has a magic wand feature that works pretty well, but again I have a feeling this can be done automatically.

Answer 1

I see I can use GD PHP's imagecolorat and cycle through all the pixels to find those that are black. This works:

<?php
$im = ImageCreateFromPNG("india.png");
$width = imagesx($im);
$height = imagesy($im);
for ($cy=0;$cy<$height;$cy++) {
  echo '<p>';
  for ($cx=0;$cx<$width;$cx++) {
    $rgb = ImageColorAt($im, $cx, $cy);
    $col = imagecolorsforindex($im, $rgb); 
if ($col["red"] == 0 && $col["green"] == 0 && $col["blue"] ==0){
    echo $cx.", ".$cy." ";
  } else {echo "";}
}
}
?>

Can anybody suggest how to find the polygons in the huge multipolygon complex that results from running the above code on say a black and white 2 color map of India, where all the borders are black and the interior of the states and Indian Ocean is white??

Here is image of India: http://wherehaveibeen.info/images/india.png and the mess now of the coordinates for the imagemap that needs to be split up into separate polygons: http://wherehaveibeen.info/images/black.php

Answer 2

An almost perfect solution to this issue is by using SVG images and this translator of the svg code to imagmap area tags: http://www.electricfairground.com/polygonator/. The result is an appropriate image map, although the svg image may need to be resized, and the countries or provinces all seem to be offset and occasionally jumbled up. So this require opening a page generated with the SVG image or exported PNG copy of the SVG file, in a wysiwig editor that allows you to move imagemap elements.

I'm trying to figure out what the pattern of the offset is and if I do I'll post it here: http://wherehaveibeen.info/images/polye.html. The author of the "Polygonator" clued me into his service and using svg map images from his article here: http://www.electricfairground.com/2009/08/08/image-map-rollover-effects-using-jquerys-maphilight-plugin/. He advocates there, the tracing of png images into svg images via Inkscape. But since Wikipedia already has maps in SVG format, why not go straight to the code? It turns out that svg files basically already have the polygons separated and the border regions speciied, at least in the Wikipedia grey maps, http://en.wikipedia.org/wiki/Wikipedia:Blank_maps, they just need some cleaning up with the Polygonator.

I found if I opened up the SVG code in Notepad++ i could copy and paste in the entire contents of the SVG file and the polygonator will remove the unneeded code. A little clean up of the imagemap area tags is required afterwards but not much. The biggest problem is the mentioned generated area tags regions offests and the occasionl jumbled up overlapping locations of the imagemap areas in the generated code.

Answer 3

Well the real answer here appears to be that SVG files are almost imagemaps already and can be mildly processed to turn them into imagemaps, and Wikipedia certainly has plenty of SVG maps.

There are at least three projects that attempt to do this, with only some success at the moment. I'm kind of more interested in making an SVG file processing online image mapper service now that so might work on that project instead of just the map coloring one:

• Polygonator - described here: http://www.electricfairground.com/2009/08/08/image-map-rollover-effects-using-jquerys-maphilight-plugin/ but the actual service is here: http://www.electricfairground.com/polygonator/index.html - is the simplest and best service or software so far I think. You have to manually dump the SVG XML text into the input field, but despite what the author says, I think you can dump the entire SVG file in the in field, not just the "M-z tag". The resulting area tags need editing to remove empty ones without coordinates and polygons with only two points.

• Inkscapemap - http://sourceforge.net/projects/inkscapemap/ - chokes on complex SVG files such as those with shading. Also I couldn't get it to display as an HTML service even though I followed advice about using the main class of the jar file which I found described in the manifest file as well referring to the main jar file and the support file in an "archive" attribute.

• http://davidlynch.org/blog/2008/03/creating-an-image-map-from-svg/ - very interesting project with many blog comments. The image maps again are not quite perfect and need editing.