The Algarve is a small rectangle +- 180 km East to West and 40km North to South. If you go too far East, except on the A22 Motorway, one will drop into the River Guadiana! To the South and West, one will drive into the Atlantic.
Driving North can be a problem BUT when one starts going through villages where there are more pigs, sheep and men wearing cloth caps, one knows one is in the Alentejo region! :))))
Furthermore, be aware that many GPS maps for the area not always up to date! I have run into this a couple of times in having to go and rescue courier companies who use GPS delivering to the home.
The region is well signposted, and with a good map, Mark I eyeball technology and asking the locals if needs be, one should have little difficulty in getting to one's destination.