Crackdown 2

This achievement can be done on any of the arenas (Hope Springs, North Green Bay, South Unity Heights). Hope Springs is probably the easiest one to do. If you're playing with anyone that has access to the helicopters (via Project Sunburst achievement), this achievement will be much easier to unlock as you can just spam flockets at the enemies. There's a certain pattern to the waves, though. Every wave ending with a 5 is a "stronghold" round, meaning more enemies. Every wave ending with a 0 requires you to capture a location by standing in a blue hexagon. The more agents in the hexagon, the faster it will be captured.
But, just so you know, this achievement doesn't specifiy the order you must play each wave in. You can jump in the middle of the match, say Zone 2, Wave 7 and play until the end. Then, if you start up on the same map at Zone 1, Wave 1 and play all the way to Zone 2, Wave 6 the achievement will unlock. So yeah, you can play the 50 waves in any order.