Recommendations for you: (1) Unless there are licensing issues, you'll probably find a bunch of useful js code you can use from OpenLayers. (2) If you can liv

Recommendations for you: (1) Unless there are licensing issues, you'll probably find a bunch of useful js code you can use from OpenLayers. (2) If you can live with a separate server process, it would be handy to just stand up GeoServer (or MapServer) and serve out WFS. ('Web Feature Service', which is served-up vector features in GML based on area of interest and other query params -- OpenLayers can parse this, which is good, because you probably don't want to write it yourself.) (This gets you a nice decoupling at the expense of being less standalone... for example, you could shell out to ogr2ogr to get your GML instead, or switch to mapserver, etc.) Edit: Reading your other comment, it seems speed is important, so maybe (2) isn't such a good recommendation, although it might be a good starting point since it will deal with a lot of the painful stuff (format conversions, reprojections, styling...) up front.