Mobile apps, geosocial networking, geo- tagging and location-based services are all parts of the geospatial revolution now spreading throughout our society. Thanks in large part to Google Maps, Bing Maps and similar popular Internet technologies; everyone is becoming geo-enabled.
At LeWeb Conference in Paris in December 2011, Marissa Mayer, Google’s Vice President of Product Management, noted that “the third-most-used service on phones, after phone calls and text messages, is mapping”. Indeed, most of us are now very dependent upon having immediate access to simple-to-use navigation tools on our location-enabled smart phones and many of us enjoy the social networking that comes from knowing where our friends are right now, or seeing on a map where the nearest “place of interest” is.
Few users give much thought to the mix of technologies, science and art that it takes to put your dot on that map. Geographers have been working on this problem for centuries. Geographic information scientists now put it all into the cloud. Accurately determining location, storing data about locations, visualizing geographic information and mining geographically-tagged information are important research frontiers and big business. Unfortunately, in the rapid development environment of the mobile app world, the fundamental sciences behind the geospatial revolution are often ignored.
Take for example the question of location. At the foundation of the geospatial revolution are the methods and technologies that allow us to determine and express where a person or place is on the surface of the earth. From school geometry lessons, we’re familiar with the idea of using a coordinate pair, usually stated in latitude and longitude, as a description of a location. And it’s easy for app developers to “map” the location of a place by simple drawing a dot in an x,y space. This leads to:
Problem #1 – Latitude and longitude are not rectangular Cartesian coordinates. Rather they are determined from a spherical grid with lines of longitude (N-S lines) converging at the poles and lines of latitude running parallel from the equator to 90N and 90S. This is fundamentally NOT a rectangular grid. These sets of lines do not meet at right angles and distances between lines of longitude varies from about 111 km per degree at the equator to 0 km at the poles. Converting distances in degrees to distances in kilometers requires spherical geometry, not our simple grade school Pythagorean theorem calculation. This leads to:
Problem #2 – The earth is a globe, so maps of it cannot be shown accurately on a flat computer or phone screen. Think of the continents drawn on the skin of an orange. Peel the skin and press it flat. The result will certainly never be a simple rectangular depiction of the continents as we see in most maps. To make flat maps, cartographers devised a large number of “projections”, mathematical transformations between lat/ long earth coordinate values and x/y map coordinate values. These transformations produce all the maps we see today. Even the spinning globe that you can view in Google Earth is a projection of a hemisphere of the earth to a flat surface. Look at the edges of that image and you will see the shapes of continents are not what we expect to see. Problems #1 and #2 lead to
Problem #3 – Unfortunately, these are complex problems that require an understanding of geodesy, geography and cartography to handle correctly. Therefore, in the throwaway world of Internet mapping and phone app development, where the 80% solution is good enough, programmers ignore Problems #1 and #2 to create a standard operating procedure in which geographic coordinates are mapped to rectangular Cartesian space. The universal “projection” for web mapping is called “Web Mercator”, but it is not a projection, it simply puts all lat/long coordinates in a rectangular grid.
So why is this important to you? It probably isn’t that important if you are trying to figure out how to get across the city. Distortions from the rectangular mapping of spherical coordinates won’t make much difference at that scale. But look at almost any web map of the world showing the distribution of resources, people, carbon emissions, etc. and you will notice, hopefully, that the northern continents are hugely enlarged. Consider how this distorts your understanding of the depicted relationships. Measure the distance between, say, Hong Kong and Seattle with a virtual ruler on a Web Mercator map and your measurements will be incorrect since distances vary across the map.
The lesson here is that while we are all quickly becoming map users, there is much more to learn about geographic information—how it is captured, sampled, stored, structured, managed, searched, analyzed and visualized. Using and sharing geographic information is extremely important in today’s geo-enabled world. Governments and businesses depend upon it to make mission critical decisions. While the web mapping world is satisfied with an 80% solution of simple coordinates and unprojections, those who depend on these technologies to manage our cities and environment must understand a range of fundamental principles that form the foundation of geographic information science. Geo-everything isn’t a new invention, there is a great deal already known and much to learn.
(See original here)
