Its at the top left of the engine, attached to the inlet manifold. You have to remove the air filter housing to get to it. If you're going to replace it, get a genuine Bosch one; I bought a cheapo one off eBay, didn't work correctly so cleaned up the old one with brake cleaner and seems to be working again.
Map sensor or maf sensor 2 different things? Mass airflow or manifold absolute pressure sensor, maps are cheaper than mafs (unless you buy a cheap maf on ebay) ive got a link of a place that does genuine bosch mafs for about 80 quid brand new, bought one myself last month really good quality