A topographical, or “topo” map is a map of an area of land that shows information on that area. As with any map, land and water are clearly displayed, as well as any roads or other notable features.
In addition to these, topo maps also show the gradient of the terrain. In effect, they are representing a 3-dimentional landscape in 2 dimensions as seen from above. To do this, a topo map shows contour lines and index lines. The distance between these lines represents a change in altitude, which is listed on the map. In essence, each contour line is actually showing a consistant altitude from sea level. An index line, is simply a bolded contour line for to make reading the map easier. These occur every 5th contour line.
For example, in the map below, which lists a 10 meter contour interval (not shown in the screenshot), a person walking from one contour or index line to the next would be climbing an altitude of exactly 10 meters. This means that when the lines are far apart, the slope is gentle (lots of distance, but very little change in altitude), and when the lines are close together, the slope is steep (very little distance but lots of altitude). Knowing this, we can start to see the shape of the land!
Topo maps also have a grid laid out overtop the map. This grid gives us a reference of where we are not only on the map, but on the entire planet. Each topographical map has its own number, and the uses both decimal and UTM coordinates, which are global positioning systems. More on this in another blog.
Topographical maps, like any maps, have their advantages and disadvantages. The main advantage is that they are extremely detailed, easy to use, free, and that they cover the entire planet. If you are travelling a river, you can simply print all of the topo maps that the river traverses, and you’ll have a detailed map. By using standard coordinate systems, they also give a reference to where you are at all times.
The key disadvantage to topo maps is that they are not annotated with any information beyond the basics of the land itself. If you are looking for information on the quality of portages, the level of rapids you may encounter, or the names of the bears that you’ll meet, these maps will not provide any of this. A good strategy if you are going to an area and plan to return is to print and laminate the maps, and then bring along a permanent marker to make your own notes.
A final disadvantage is that these maps are often hopelessly out of date. Unlike mapping software, these maps are not updated regularly. In most cases this is irrelevant, since the land changes very little over time, but in some cases, such as rivers that may change course, this can cause minor inconveniences.
If for whatever reason you are using it for driving directions, I would suggest sticking to the internet.