Topographic maps supply a general image of the earth's surface: roads, rivers, buildings, the relief (the elevation or depression), and the names of the various mapped objects. Topographic maps are most often characterized by the contour lines. Contour lines are lines drawn between points with the same elevation. Because the Earth’s surface is continuous, all contour lines are continuous and do not have an end.
Topographic maps are useful when the ground features are important to your project. They show water features and the contour lines illustrate the gradient of the surface in question. If the vegetation coverage or anything above the surface is important to your project, then you may be better suited by an aerial image.
The lines on a topographic map are called contour lines. Contour lines connect points with the same elevation. If you were to move along a contour line, you would never change elevation. By moving perpendicular to the contour lines, you would either be walking up or down hill.
Topographic maps tend to be older because the geographic changes of the Earth tend to be minimal over any sort of measurable time with the exception of natural disasters. Because of this and the intense amount of work required to develop topographic maps, they only tend to be updated whenever necessary.