The ads can be placed on the maps themselves or you can use lat49's off-map ads. These come in a number of sizes such as Leaderboard (728x90), Medium Rectangle (300x250), and Full Banner (468x60). Both the map ads and the off-map ads are geo-targeted and are directly related to the users' interaction with the map.
This week lat49 also released a new API for Flash-based maps/mashups. So if you use the Google Maps API for Flash it is now possible to integrate the full functionality of lat49 quickly and easily. As with the lat49 Ajax map API, ads can be displayed either on the map itself, or off-map.
Google Maps developers can also use Google's own AdSense programme via Gadsmanager. Gadsmanager serves geographically relevant ads as small tags on Google Maps. Map developers earn revenue from the maps when users click on the ads.