Like I know that discoveres sailed around a continent and roughly drew the coastline but HOW IN THE HECK did it work, Australia for example is so huge that I cannot fathom the fact that human beings managed to draw and reproduce physical maps before satellites existed. Or were maps just very inaccurate compared to today, but detailed enough for everyone to get around?
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They were pretty inaccurate for a long time.
On land, you can determine how far away things are from each other and at what angles you see different landmarks. You can extend that to a whole network of points and sight lines and draw a map from that.
You can also determine your latitude (north/south) accurately by tracking the Sun or the stars. With a good clock and by watching the Sun, you can measure your longitude (east/west) in addition. That lets you find the relative alignment of things you can’t see together, like other continents or remote islands.
Maps of coastal outlines can be pretty accurate once someone understands trigonometry and has a compass and a telescope. Using triangulation, it is relatively straightforward to build a fairly accurate 2D map.
You are right that interior maps of places like Australia were far less accurate initially simply because not a lot of people ventured there. But soon enough, someone would venture in and do the measurements necessary to create more accurate maps. And yeah, “accuracy” is sort of hit and miss initially since many early explorers sort of “filled in the gaps” – with some rather bad assumptions at times (rivers and lakes that don’t exist). With more and more exploration, the errors were simply corrected over time.
In any case, even things like “very inaccurate” are not meaningful. Would you, for example, “care” that Beijing is 10km north of where it is shown on a map. Or that Guam island is 10km to the west etc. To 99.9% of us, these inaccuracies are irrelevant.
Trigonometric surveying. Basically, you choose your ‘point zero’ on any given landmass. You get one guy to stand there with a theodolite (which is a spotting scope that can measure angles of elevation and deflection); and you get a bunch of other people to wander off towards other points holding targets on poles. You then sight the target, note down the range, elevation, and deflection. Do this for every point of interest you can see from your original point zero, then move to each of your survey points, and repeat til you’ve covered the landmass.
Yes, it’s labour intensive and extremely time consuming, but that’s how it was done. Interestingly, this is why the official cartography company of the UK is called Ordinance Survey: the maps were drawn for war planning.
First maps were very inaccurate. But navigation required accurate maps, both in avoiding rocks and shoals as well as reaching destinations. The reason speeds on water are measured in knots were these were physical knots in rope used to measure distances and speed which improved early map making, then accurate time pieces enabled calculation of long distances. It wasn’t as if suddenly people had good maps, it took a lot of small improvements over a long time.