Читать книгу Geography For Dummies - Jerry T. Mitchell - Страница 115

Few things are more important in cartography than the positional accuracy of mapped objects. Historically, this was accomplished by field observation. That is, explorers or surveyors would travel to a particular area, observe locally important features, and map their locations. Nowadays, GPS (global positioning system) technology has greatly contributed to positional accuracy. Think about exactly how accurate our spatial data needs to be for self-driving cars to work!

While you may think of GPS as the nice voice that gives you directions in your car, have you ever thought about the system that makes it all happen? The United States has launched a series of satellites (31 operational at the time of writing) that talk to a GPS receiver, often now in your smart phone. The United States is not alone here. Russia, China, India, Japan, and the European Union all have systems, so geographers are now likely to refer to a Global Navigation Satellite System to encompass it all.

Using trilateration — or measuring distances — the receiver and satellite bounce signals between each other and record the time the signal takes to be read. With three satellites doing the same thing, we can accurately locate you on Earth by putting you in the middle of a satellite Venn diagram. Add a fourth satellite and we can determine your elevation.

There are a number of really neat smart phone apps that allow you to collect data with accurate locations and other ones that allow you to get outside and play (and I mean, play!). Try geocaching some time, where you use GPS to undertake little treasure hunts. You’ll learn something about your local environment, engage with cool technology, and probably get some exercise at the same time. What could be better?