On the OpenShift blog Ryan Jarvinen has a new tutorial showing you how to use MongoDB and Silex to create a basic mapping service. It takes advantage of the MongoDB spatial data and query functionality to help locate and map items from the dataset.
He starts with a look at the datastore - the MongoDB - and the kind of data it will contain. He's shared the dataset (and complete example code too) over on Github and includes the command to import it. He then starts in on the PHP side of things, showing you how to get Silex installed and add in some basic routes and CSS. He then uses the Leaflet.js library to import the data and drop it into an Openstreetmap-based map. The full code and data can be found in this repository over on Github.