Understanding the Global Positioning System (GPS) requires more than a passing familiarity with maps. Maps are indispensable to genealogists. Some genealogical relationships defy analysis without the ability to place the events on a map. Likewise maps show relationships that might not be obvious otherwise. The most common issue is boundary changes. The shift of a boundary by a few miles can place a family in a different county or even a different state. Maps must also be wedded to history. Any map is a snapshot in time. Streets are renamed, buildings disappear, rivers change their course, entire countries vanish. GPS technology does not replace maps, it only augments our ability to use them.
We are all in the map business even if we draw a simple map to show directions to a store or library. The Internet and GPS devices have made more of us aware of the complexity of maps. Google maps and Google Earth have opened up a whole world of maps to anyone using a computer on the Internet. As genealogists we need to understand some of the fundamental principles of maps and map making so that we can learn from the vast wealth of historical maps online. In the U.S., at the very least, all genealogists should also be familiar with The National Map and the wealth of information available on topographical maps of all kinds. The geographic information available from The National Map includes orthoimagery (aerial photographs), elevation, geographic names, hydrography, boundaries, transportation, structures, and land cover.
Except for very small areas of the earth, map makers (cartographers) have struggled since antiquity to represent locations on a sphere on a flat map. (The idea that historically people thought the earth was flat is mostly a myth, but that is another post) Physical globes are very limited in their size, very large globes like the one at the National Geographical Society headquarters are interesting but not very useful for genealogists working at home or in a library. GPS devices are really good at showing specific locations but depend on maps to show relationships and surrounding points of interest.
I am always surprised at how many people just don't understand maps but having a firm understanding of how maps represent the earth's surface in time and space is a necessary prerequisite to adequate genealogical research. If I am given a genealogical problem to solve, my absolute first reaction is to locate the events on a map. Without doing so, I would be risking starting the research without a firm understanding of the question being asked. I am reminded of the lady I worked with who insisted that her family lived in Pennsylvania. I found a family with the same names for the father, mother and children living in Ohio, but she refused to even consider the information because her family lived in Pennsylvania. I looked on the map and the family in Ohio was living only less than 20 miles from the Pennsylvania border. I wish I could say that this information helped to convince the lady that she should consider this family but she dogmatically continued to insist that her family lived in Pennsylvania.
Let's assume you purchase a GPS device online or from a local store. You learn that a cemetery is located at certain map coordinates. If you enter the coordinates into the GPS it will likely give you a route to the location of the cemetery. What now? Well, I would suggest that you should look for those same coordinates on some maps perhaps online, perhaps on paper. I would further suggest that you would want to know a lot about the surrounding area and whether or not the route selected by the GPS was practical. One time while we were driving to a location in Texas, the GPS device in our car kept telling us to turn right at every intersection. The problem was the road the device had selected was under construction and blocked off. Had we used a paper map, we could have found an alternative route but the GPS gave us no options. Just as you should not rely on a single source to entirely establish a genealogical fact, likewise you should use a variety of map resources, even if you have a GPS device.