World map with parallels
Now imagine a very small square piece of land at latitude On the map the parallels are all the same length. The equator is a circle with radius (the radius of the Earth)Īnd circumference, and the parallel at latitude is a circle of radius Here is a picture of the Earth with the top sliced off at Is, in units where the equator has length on the map. Let's say that the distance on Mercator's map from the equator to the parallel at latitude
![world map with parallels world map with parallels](https://i.pinimg.com/originals/45/d2/6a/45d26afcd015baf1858c6cc5bd72c806.jpg)
In 1599 the English mathematician Edward Wright explained the mathematics of exactly how Mercator's projection should be done. The cylinder when it comes into contact with it. If you want a physical model of Mercator's projection, let the globe beĪ spherical balloon that is blown up inside the cylinder, and sticks to This cylindrical projection is NOT Mercator's projection.
![world map with parallels world map with parallels](https://geology.com/world/cia/map-of-africa.gif)
The globe onto the cylinder, as in the picture here. The idea is to imagine aĬylinder with the globe inside, and light projected from the centre through
![world map with parallels world map with parallels](https://www.worldatlas.com/upload/0e/42/4c/world-map-mollweide-projection.png)
This seems to be commonly taught in high schools. Many people have an incorrect idea of how Mercator's projection works. It is for these reasons that we have progressively increased the degrees of latitude towards each pole in proportion to the lengthening of the parallels with reference to the equator. He almostĬertainly didn't have a formula, but might have done it using approximate measurements on a globe. Mercator knew that to give his map this desirable property, he had to make the lines of latitude farther apart as you go away from the equator. This method wouldn't work there: rhumb lines would be curves. If you keep heading in this direction, you ought to get there.Įarlier maps were drawn on a simple grid: each degree of latitude or longitude is the same size. So (after a small detour around Vancouver Island) you head southwest, and off you go. Just draw a straight line on the map between where you are and where you want to go, and measure the angle (almostĮxactly 45 degrees in this case). Vancouver and want to get to Honolulu, Hawaii. Lines of constant compass heading (called rhumb lines by sailors) are straight lines on this map. The property of the Mercator projection map that made it useful to navigators is that it preserves angles. The Mercator projection was invented by Gerardus Mercator, a Flemish mapmaker. A developable surface is the geometric shape that a map projection can be built on.Īctually, some map projections don’t use developable surfaces at all such as the Goode and Bonne projections.Mercator's Projection Mercator's Projection It uses an equation to transform Earth’s angular geographic coordinates to XY Cartesian coordinates using developable surfaces. But when we use map projections, we locate positions in meters or feet. When we locate positions on a sphere, we use decimal degrees. If you can imagine you are cutting an orange into 60 wedges, this is how the UTM system works.įrom here, it assigns the central meridian a value of 500,000 meters.
![world map with parallels world map with parallels](https://i.pinimg.com/originals/a7/4d/70/a74d7037ab22a68bcd1837d159ce9b96.jpg)
For example, the Universal Transverse Mercator system splits the Earth into 60 sections by lines of longitude. For example, New York’s position is (40.714°, -74.006°).īut when the Earth has a map projection, this means that it has projected coordinates. This is our geographic coordinate system. Remember that with a sphere, we use latitude and longitude to pinpoint our position.