Instructables

gps transmitter chip + tracking software (google maps) possible?

is it possible to purchase a gps transmitter chip (smallest possible battery) and have it "upload" its locations in real time on google maps?

chip and power source should be as small and thin as possible to fit in envelopes or packages.

You won't be able to fit one into an envelope. But what your talking about is a GPS locator deacon like this.
http://www.ems.com/product/index.jsp?productId=11324657&emssrcid=GoogleBase:PS11324657

These things are about the size of a small flip phone. You need more then just a GPSr chip. You also need the hardware that takes the satellite signals received and translate that data into Lat and Long. Then it needs hardware to connect to the internet (probably through 3G cell phone service) and report those coords to a web service that can then give you a map tracking the location of the device. So building one yourself may be a bit much.

As you can see these things are not cheap which is why sipping services use bar codes and RFID tags to track packages as they go from one depot to another and from truck to truck. Any other option is too costly to maintain.

If it has to be smaller and cheaper and you can do without real time logging then you can get a GPS data logger. This one here is about the size of a pack of Orbits gum.
http://www.amazon.com/DG-200-GlobalSat-Logger-Windows-Compatible/dp/B0057AKAYO