Often not very well!!

The accuracy of maps made without a deliberate surveying system with appropriate tools was often patchy and based on walking times, sailing times, and people literally pacing distances often without direct lines of sight.

The actual tools to conduct an accurate survey aren’t that complicated, they just require equipment built to very high tolerances along with some basic knowledge of trigonometry and material properties such as thermal expansion.

Once these systems were developed and governments had incentive to outlay the significant funds for surveys the accuracy improved a lot - such as the Great Trigonometrical Survey of India - an endeavor that involved a considerable number of people almost 70 years painstakingly measuring triangles across India.