Spycraft has a good way of dealing with environments in their chase system. It's not overly complex, but does the job.
It comes down to designing different chase moves, giving them Ride DCs based on how good they are, and then assigning penalties based on how difficult doing those maneuvers is in a densely packed forest or city street vs a wide open plain. At that point, it becomes a game of paper-rock-scissors-sword-crossbow-tuna-apple... Apple beats Tuna, Rock beats Tuna better. It's harder to do Rock than it is to do Apple... and doing Rock in the slums is tough.
After that, you define how far apart chasers must be to effectively end the chase.. in the plains it may be based on distance and time (after 5 hours, they give up) while in the city it may be based on losing them (after minutes, or simply a really high DC check that must be made at a certain distance, resulting in an automatic chase win).