How to design markers - raster or vector?

Question

I have several layers that are point geometries. I am defining them custom markers symbols and such symbols have colors (red, yellow and green) to represent values.

Since there are several of them in an area, I started with marker clusters, but quickly realized that clusters are good only if all markers mean the same (like redfin home markers).

I would like to stick to markers but to avoid visual clutter - I would like to resize them based on the zoom level. If I design these markers in SVG, I could achieve this - as its easy to size SVG than raster formats, similar to this link http://mapbox.com/tilemill/docs/guides/advanced-map-design/#images_as_icons

Please send me any examples or sample sites you have developed or come across so that I can see the visual appeal of having several custom markers in maps.

Thanks, Ramesh

Answer 1

In my application I am using PNG images to represent the markers and use Rules, added to the Style of the layer, to set their size based upon the zoomlevel.

var markerStyle = new OpenLayers.Style({
    externalGraphic : '${imagePath}',
    pointRadius     : 15
});

var markerStyleMap = new OpenLayers.StyleMap({
    'default' : markerStyle
});

markerStyleMap.styles['default'].addRules([
    new OpenLayers.Rule({
        minScaleDenominator : 10,
        maxScaleDenominator : 4999,
        symbolizer          : { pointRadius: 15}
    }),

    new OpenLayers.Rule({
        minScaleDenominator : 5000,
        maxScaleDenominator : 9999,
        symbolizer          : { pointRadius: 10}
    }),

    ...
]);

var layer = new OpenLayers.Layer.Vector("markers", {
    projection : "EPSG:900913"
});

layer.styleMap = markerStyleMap;

The URL of the image representing the marker is set as an attribute on the feature and can be referenced by using the ${imagePath} notation in the style :

var marker = new OpenLayers.Feature.Vector(pointGeometry, {
     id        : markerId,
     imagePath : '...url of the image to use...'  
});