Very cool! I didn't find the link to the data though.
How big are 20M worth of data points? I guess there is are two coordinates (or maybe box) and then a label. It could be several gigs.
I think if you are truly open and not just promoting your API you should allow for a direct download of the entire data dump.
Perhaps you can use "requester pays": http://docs.amazonwebservices.com/AmazonS3/latest/dev/index....