While the preceding description is accurate, it doesn't really help us much. As befits a field concerned with the lay of the land, GIS really begins in the field. Data is gathered using aerial and satellite photography, and it is also gathered from people on the ground using GPS, laser range finders, and surveying tools. GIS can also make use of existing maps, especially for historical research and to compare time periods. For example, this may involve studying how a city has evolved over time or national boundaries have changed. A lot of time and energy in GIS goes into gathering this data and entering it into the computer.
Once the data is in the computer, GIS can perform a wide range and variety of analyses on the data, depending on the questions being asked and the task at hand. For example, the following are some of the many things you can do with GIS: