Another map essential is the title. A good title will tell what, where, and even when. The title should give enough information to describe what is shown on the map. Since maps may be historic and have a long shelf life, the when part of the title can be essential, not just beneficial. A map of the U.S. Population, 1900 is quite a different map than a map of the U.S. Population, 2000.
Another essential is the date. A map should always include the date that is was first published, and ideally, the dates that source materials were gathered. The date of production is often not the same as the date represented by the mapped data. A map of the U.S. population in 1800 produced now would be notably different than a map made in 1808. A map of U.S. Population, 2000 produced this year might be based on an estimate from 1999 or might be based on preliminary data from the census taken in 2000. These imply different levels of accuracy. Even in using a city map, the date is important. While doing my dissertation work, I obtained a map of Indianapolis, Indiana. Some time later, I was trying to get to the location of the map and globe making company, Cram. I had identified their location on the map, and knew where I was; however, since the production of the map, a new interstate highway had been built between where I was and the company several miles away. With map in seat beside me, it took me many dead ends and busy intersections before I found a way around the highway and to my destination. As new roads are added in new subdivisions maintaining the currency of maps is a major concern, and an important source of employment and job opportunities for geographers. Updating of maps is often done through photorevision. This means that, instead of the costly and time-consuming process of having a geographer travel to an area and spend a week snooping around, the maps are updated quickly and cheaply (but not as accurately) by looking at aerial photographs. And many cities, towns, utility companies, and businesses are converting their maps to digital forms and digital databases that can continually be updated and revised and used for spatial analysis to solve spatial problems. This is the growing field of Geographic Information Systems or GIS.
Along with the importance of the date information is the source information. You cannot just sit down at your desk and draw a useful map, making it up as you go along. You need to have lots of information about many different subjects, including the topography, the condition of roads, political boundaries, the location and names of towns, among many other topics. The "source" lets the reader know where you got this information. A single map may be compiled (put together) from many different sources. For example, the source may have been "field checking", that is, someone actually got out there and looked around. Other sources might include older maps, books, aerial photographs or satellite images. It is important to know the source of a map so that you can know how it was made and how accurate it is likely to be.
Name of the cartographer / publisher
The name of the cartographer, or agency, that created the map is always included. This is to give credit to people who have done a lot of good, hard work, or so that we can bad-mouth people who have made poor maps.
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