And before anyone says it is too hard to produce a map, it is quite easy.
First, observe that the sun makes a cyclic appearance, that is it takes roughly 24 hours to return to the same position in the sky.
Using this we can determine the longitude of any point.
Using the observation that on the equinox for the equator the sun rises due east, goes directly overhead and sets due west, we can note that the equinox needs to be a straight line or a circle curving into the ground.
So the last part is distance from the equator (or latitude), and that can be determined by measuring the angle of elevation of the sun and some simple trig.
Using this you should be able to produce a map with one x scale and one y scale.
An alternative to measure latitude is to not that Polaris is directly above the north pole, or the south celestial pole is directly above the south pole.
Using this, and the fact that the sun circles the North/South pole, you know the north/south pole must be the centre of this flat Earth. (I know, 2 centres makes no sense, that is a problem with the FE, not reality).
Then, you can use the angle of elevation to the north/south celestial pole to determine your latitude using the same simple trig.
Then you just need to plots these out to make a map.
Here is a google sheet to help:
https://docs.google.com/spreadsheets/d/1iwFa5a2VFkpS9Smv60xKAT1iTXZDDsg6G_tw61bdRm0/edit?usp=sharing