[OpenLayers-Users] Proportional Symbol Mapping

[Bjorn Sandvik]

Thank you!

The circles are now scaling properly on each zoom level:
http://thematicmapping.org/experiments/openlayers/propsymbols_stylemap.html

How can I adjust the hover effect (keep the same size)?

Bjorn

Andreas Hocevar wrote:
> Bjorn,
>
> your requirement is covered by the new OpenLayers.StyleMap.
>
> First of all, have a look at the styles-context example 
> (http://www.openlayers.org/dev/examples/styles-context.html). The 
> second example there (the points in the southern hemisphere) are 
> created with an advanced template. The same can be done for your use 
> case.
>
> If I take your original code for the calculation of the size:
>
> feature.style.pointRadius = 3 + (pop * (40 / 1312978855));
> feature.style.fillColor = feature.attributes['colour'];
>
> I can create the following template:
>
> var context = {
>    getSize: function(feature) {
>        return feature.attributes["population"] * someFactor * 
> map.getScale();
>    },
>    getColour: function(feature) {
>        return feature.attributes["colour"];
>    }
> };
> var template = {
>    fillOpacity: 0.9
>    pointRadius: "${getSize}", // using context.getSize(feature)
>    fillColor: "${getColour}"  // using context.getColour(feature)
> };
>
> var style = new OpenLayers.Style(template, {context: context});
> vectors = new OpenLayers.Layer.Vector("Vector Layer", {
>    styleMap: new OpenLayers.StyleMap(style)});
>
>
> You only have to find an algorithm to derive your pointRadius from 
> (using map.getScale() or map.getResolution() and someFactor).
>
> Also, there is no need to set any feature styles in the onload method. 
> You're all set with the above definition of the styleMap in the 
> constructor for your vector layer.
>
> Regards,
> Andreas.
>
> Bjorn Sandvik wrote:
>> My question: Is there a way to keep the relative size of the symbols 
>> when the users zoom in/out?
>> (symbols should keep their size relative to the size of the countries).
>>   
>
>


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