April 5 is National Read a Road Map Day.
When Columbus set out from Spain, he was convinced the world was round, but he was way off in terms of what the globe actually looked like. In his case, it was because he didn’t have enough information.
Today, we all have continuously available information about the world around us (with GPS enabled smartphones), but fewer and fewer of us know how to read a map. If you found a treasure map, would you be able to find the treasure if you couldn’t put the address into your phone? What about if the GPS system suddenly went down?
Columbus navigated by what is called “dead reckoning.” In dead reckoning, you measure your course and speed, and then mark a map based on your last known location. A compass, a measuring line, and an hourglass were all he had.
Later navigators became adept at measuring their latitude, or distance from the equator, using the stars. Celestial navigation, as it is called, allowed eventually for very accurate measurement of latitude.
Measuring longitude, however, is much more difficult. In the days before GPS, the useful measurement of longitude required a very accurate clock. In the middle of the 18th Century, John Harrison, an English carpenter, finally succeeded in producing an accurate enough marine chronometer to meet the requirements of sailors. While his specific invention was never widely used, marine chronometers became the standard tool for measuring longitude until the advent of GPS and other radio-based systems.
- What does it feel like to be lost? Have you ever been truly lost? Lost in the sense, where you don’t even know in what direction to go to find a landmark?
- For fun, find a road map and try to measure the time it will take you to get to a nearby town. Do you know how to do this? Next, put the name of the town into your phone and see whether your time matches your map software’s time. To what do you attribute any difference?
- In some Midwestern states, county roads are built along map lines and evenly spaced. Many towns have a street named “Meridian,” to indicate the starting point for this. As you go north, the distance between longitude line-roads shrinks due to the curvature of the earth. As a result, the area of land in between them also shrinks. Because surveyors were asked to create land plots with a fixed number of acres, to correct for curvature, north-south roads sometimes “jig” or “jag” a few yards. Do you know of a road like this (where a straight road suddenly ends, and then continues straight again, but shifted East or West by a few yards? See if you can find one on a map.
28, Mar. 2018, World Map 1492 [Digital image]. Retrieved from <quora.com>.