Cisco's outdoor mesh is not a new concept, but a different animal than the indoor world. You can cover much larger areas with fewer APs. Be warned, just because you can 'see' the AP from a location doesn't mean it can 'see' you. the 1550 series APs have a much greater sensitivity than lets say the 3600 series. The external omni-direction antenna can detect down to the range of -92 dBm. The real limiting factor is going to be your clients. Laptops at 'full' power will get you a lot further then your average Moto handheld scanner, iPhone, etc. There is lots of good info out there, but some of it is hard to find.
Here is a list of documents that are very useful for mesh deployments:
Cisco 1550 Ordering Guide
Cisco Mesh Deployment Guide 7.3
Cisco Mesh Deployment Guide 7.4
Cisco 1552 Range Calculator
