Ipod App - GPS System of London

Hi, I would like to hire an app developer who can make one of numerous projects for me. The idea: I would like to make a GPS app where you can change the background. The GPS location will only cover London. The Idea is you can enter a postcode and the app will show you where you on the background based in proportion to the GPS. This is all that I would like to be done for now so its incredibly simple I think. The app should be able to made easy for further expansion; I.e to add times, distances of certain icons, add a compass system with alarms and so on. Please contact me asap as I want to trial this out. Thanks