Automatic Packet Reporting System (APRS) is a system developed by Bob Bruninga, WB4APR. It uses amateur radio to transfer weather reports, position reports, and messages between users.
To quote Bob Bruniga, its inventor, 'APRS can be summed up with two concepts, Real-Time Packet Tactical Communications, and Maps. Presumably, 98 % of APRS potential does not require a GPS or any tracking device. Consider APRS as just a multi-user assigned packet network with a Map display for many unknown amateur applications.'
It is tough to define APRS, because of its versatility of application. Primarily, APRS uses AX.25 UI packet frames to report position and telemetry. APRS digipeaters rebroadcast the UI frames, usually, on the same frequency they receive them. There is a designed-in technique for transmitting packets by using the UNPROTO path of all APRS TNC's (terminal node controller). APRS ordinarily uses both HF radio frequencies (at a 300 baud data rate), and VHF radios (generally using a 1200 baud data rate).
APRS can make use of old crystal regulated VHF radio transceivers, TNC's, and 286 PCs or even XT's. Except for a few applications, you do not need a GPS where they are a basic necessity. There are certain applications for which you would need a PC online for some you don't. Not necessarily you would need to be in a vehicle to use APRS, but it works best there. It also works if you are walking, biking, boating, or skiing, or even if you end up being in your basement. Besides giving an opportunity to use some of the old equipment, there is also a large variety of state-of-the-art, new equipment which is meant for APRS and similar activities.