Interesting, and useful info. I am developing a similar application with a map and live data generated dynamically by my server. The difference with my app, is that the data will be global, not for one city. The Citi Bike Map appears to load all of the data available regardless of map extent, which can be practical with a small dataset. How do you deal with caching when the extent of the user's map is constantly chan…
You should look into vector map tiles! Basically, you create a little JSON snippet for every image that the map server returns, and then overlay it in the client. There's support for JSON tiles in Polymaps ( " rel="nofollow">http://polymaps.org/> ).
Do you have any recommendations on how to create the tiles?
The most important thing, is that when a user clicks the markers in my map(whether or not they are real vector markers or rasters passing themselves off as markers), the marker's associated attribute values need to be available to be fed into a popup.