The way OpenLayers puts markers on the stage is fine when they are not so much, but once you need more than 100, the library’s solution is not good. The question is is there a way to put all the markers faster than the built in method.

Yes, There is a Way to Speed Up Markers Load

I once wrote about how to speed up markers on OpenLayers, it is clear that my decision was to concatenate the DOM elements like a string after I’ve generated all the markers as markup with innerHTML as it’s faster than appendChild. The only question left is how to convert Longitude/Latitude pair in pixels.

The Answer’s Given by OpenLayers

There is a method called getLayerPxFromLonLat() which do the job. Let me show you a snippet:

ll = map.getLayerPxFromLonLat(new OpenLayers.LonLat(lon,lat));
console.log(ll);

You can see what’s inside the ll object. You can now reference the pixel as ll.y and ll.x.

Following several posts I wrote recently, this one will describe you a simple and robust tutorial how to optimize OpenLayers. My goal is pretty simple. I’d like smaller library but still with everything must work correctly. The fact is that OpenLayers comes with more that what I need so I’m going to exclude some files from the build process.

Step 1

This procedure I found here, and what I made is to copy/paste the whole list described there. The problem is that immediately the application stopped working, but in the same time I could catch what errors were stopping it and simply I was able to include again those files needed by my application.

Step 2

Even when I excluded everything from the library, there are some files I don’t need but that enter the resulting build. That’s because they depend on classes I need and the builder is simply adding them. The solution, even stupid enough, is to comment them all.

Note that on every step you need to check if the application is still fully functional. That’s a bit annoying, but it comes on the price of faster app.

Step 3

Change the compiler! Actually now OpenLayers is using JSMin, but I personally use Google Closure Compiler with it’s default level of optimization. Thus the resulting OpenLayers is 312K and still fully functional. After GZip it becomes even smaller and the load time is pretty good.