system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How did cartographers make maps back in the day?

How did they know what the shapes of the continents were without satellite imagery looking down on the planet?
gpt
If you have a way of figuring out latitude and longitude of points where you are (doesn't require a satellite network) you can sail along a coast and take readings every so often.  The same thing is true if you just have a way of measuring directions reliably (e.g. if north is 0 degrees and we go counterclockwise 90 degrees would be west you would need to be able to give the direction in degrees to a certain level of accuracy) and distances.