Why APRS is an AX.25 packet network, usually on 1200 baud AFSK at 144.390 MHz in the US. Coverage is extended by digipeaters, stations that receive a packet and immediately retransmit it on the same frequency, with the path set by aliases such as WIDE1-1 and WIDE2-1 that limit how many hops a packet takes. This unconnected (UI frame) broadcast approach lets one beacon reach many listeners and Internet gateways without any point to point link setup.
Watch out The choice about ACK/NAK relay describes connected-mode packet, where each frame is acknowledged; APRS deliberately uses unconnected beacons with no acknowledgment. C4FM and DMR are digital voice modes on their own repeater systems and do not carry standard APRS packets.
APRS = packet, and packet repeaters are digipeaters. Think WIDE1-1, WIDE2-1 hops on 144.390.