Interactive maps with Leaflet

One of my current side projects involves visualizing crime activity in St. Louis and other cities. A key component to the project is being able to represent the density of crime incidents on a map, and so I've been exploring open source mapping API's. The best one I've come across so far is a Javascript library called Leaflet for displaying interactive map layers. The above is an example I created using an OpenStreetMap layer, with a popup marker I placed pointing to my favorite part of City Garden in St. Louis.  

My end-goal is to build an iOS app with an interactive elegant crime map. In the coming weeks, I'll use my blog as a testing ground as I explore the various features relevant to my project. The next thing I plan on doing is pulling in a GeoJSON dataset with block-level polygons color-coded by level of crime activity.