Map projections and why they lie
A sphere cannot be flattened without stretching, tearing or shrinking something, so every world map is a choice about which lie to tell. Knowing which one you are looking at explains most of the misconceptions in the scale section.
What was the Mercator projection actually designed for?
Holding one compass heading
Gerardus Mercator's 1569 projection lets a navigator draw a straight line and hold one compass heading. The area distortion is the price paid for that property, not a mistake.
Source: Mercator, 1569; standard cartography
Why can no flat map show the Earth without distortion?
A sphere cannot be flattened
Gauss's Theorema Egregium proves a sphere has intrinsic curvature that no flat surface shares. Every projection must sacrifice area, shape, distance or direction.
Source: Gauss, Theorema Egregium, 1827
Why is north at the top of most maps?
Convention, not any physical necessity
Medieval European maps often put east at the top, and some Islamic maps put south. North-up spread with European navigation and printing, and there is nothing physical behind it.
Source: History of cartography scholarship
What is 'Null Island'?
A buoy at 0,0
There is no island at zero latitude, zero longitude: only a weather buoy in the Gulf of Guinea. Databases with missing coordinates default there, so it appears heavily populated.
Source: NOAA PIRATA buoy network; GIS folklore
Why do some maps contain streets that do not exist?
To catch copying by rival mapmakers
Trap streets and fictitious entries prove plagiarism if a competitor reproduces them. Agloe, New York, was a fictional town that later gained a real building.
Source: Cartographic copyright litigation; the Agloe case
The Gall-Peters projection became popular because it does what?
Shows true areas
It is equal-area, so it corrects Mercator's inflation of high latitudes. The cost is badly stretched shapes, a trade cartographers still argue about.
Source: Arno Peters, 1973; cartographic responses
On a topographic map, closely spaced contour lines mean what?
Steep ground
Each contour joins points of equal elevation, so lines crowd together where height changes quickly. Widely spaced lines mean gentle slopes.
Source: Standard topographic map conventions
A compass points to magnetic north, but maps use grid north. What is the difference called?
Declination
The difference varies by place and drifts over time, which is why map margins print the declination and the year it was measured. In some places it exceeds 20 degrees.
Source: Ordnance Survey and USGS map conventions
The oldest surviving map showing the whole known world comes from where?
Ancient Babylon
The Imago Mundi, a clay tablet from around the sixth century BC, shows Babylon at the centre of a circular world ringed by a bitter river.
Source: British Museum, Babylonian Map of the World
How often does 'here be dragons' actually appear on historic maps?
Almost never
The phrase in Latin appears on the Hunt-Lenox Globe of about 1510 and almost nowhere else. Mapmakers did draw sea monsters, but rarely wrote that.
Source: Hunt-Lenox Globe, New York Public Library