It has nothing to do with the chip. This is all about how the software is optimized, for either handheld operation, or for driving operation. Some dedicated GPS units (like Garmin) have a software setting that allows you to use it in different environments (walking, biking, in a car) and it's all about changing a software setting that optimizes calculations for the type of usage. The iPhone maps don't have such options. That's why I said it works better when driving. The difference between street and driving is because when you are driving, the software assumes you can't go off the road and it self correct minor errors that way and it expects moving speeds similar to car speeds. When walking, it knows you can go off roads or in random directions and takes that into consideration, plus it knows you can't go too fast because you're walking. This helps correct any errors.