Reading a Topographical Map


At the behest of a friend of mine, Alison;  whom desperately wishes to learn how to read a map, and use a compass, I will begin a few posts regarding Navigation. I want to focus first on reading a topographic map; mostly because you can navigate a lot easier with just a map, than you can with just a compass. (GPS is just plain cheating!)

Map Features

The first order of business is to be able to identify the features on a map, once you can identify the features, and what they mean, a map begins to become useful. Contour lines, river markings and other similar features allow you to plan a trip that will allow you to cover distance easier, make sure you achieve the highest possible points in an area, avoid these heights or make sure you detour via water sources. Knowing what surrounds you, allows you to get the most out of a trip.

Contour Lines

Contour lines are always subject to the legend of the map, but the concepts stay the same, for every line, there is an associated ascent. ergo, should you have a lot of lines close together, this means a steep hill, versus long distances between lines which means a slower ascent.

In the example below the walker who takes the blue line, has a steeper initial walk toward the peak, before mounting a very steep face where there is an almost 20M climb, then travelling along the razorback it is quite flat, less than 20M up or down before walking to the top of the peak at 360. A walker on the red line, would have a very flat initial walk, then gradually stepper before a consistent angle for the latter part of the walk, getting slowly steeper. Every time either walker travels over one of those lines, they have covered 20M of vertical distance between that line and the last.

Topographical Map

Scale

Scale too is important, what is depicted above could be very different walk depending on the scale of the map, it its a 1:30,000 map, one centimeter on the map is equivalent to 30,000cm, 300M. If the scale was 1:50,000 the distance becomes 500M per centimeter on the map. the decisions that are made by the hike planner could be very different. on a 1:30,000 map, the Blue hikers walk would be very difficult, if not impossible, but on a 1:50,000 it would much more likely be possible.

Lat/Long

Latitude and Longitude lines, (not depicted on the map above) allow for co-ordinates to be designated to all locations on earth on a unique basis. Latitude lines run east to west, while longitude run north to south. In lat/long coordinates; the lattitude comes first followed by the longitude.

Latitude is measured from the equator with a directional symbol, the Equator is 0 degrees. Latitude is measured east and west with 0 degrees at Greenwich in England (the same place that GMT or Greenwich mean time starts and counts to 180 degrees). After the first measurements, both are broken into minutes and seconds in 60 unit intervals to increase accuracy even further.

For example, Melbourne, Australia is 37 degrees 47 seconds south, 144 degrees 58 seconds east

Latitude and longitude can also be depicted as decimal, most GPS in todays market can give you both types of co-ordinates. Most maps will allow you to get your accuracy down to accurate minutes, with a ‘guestamation’ on seconds.

Cathedral Ranges

A latitude and Longitude grid over Cathedral ranges; with measurements down to seconds

Orientation

Orienting a map is quite useful and actually quite straight forward. It can be done using a compass if you have one, you simply find the magnetic north line, orient your compass to north and hurrah you have a correctly aligned map. Without the compass however, using large and distinctive features such as peaks or rivers can help you align the map; i usually try to triangulate my position using three features roughly the same distance apart(in a 360 degrees sense) , once aligned, you can use the map to figure out where you are and where you plan on going.

Magnetic Declination

Magnetic declination is the difference between magnetic north and true north. I will cover more in compass navigation as it doesnt affect reading a map; however it is very important when using a compass to align a map as it give us the difference between magnetic north and true north. Suffice to say for now, that due to the way the magnetic fields of earth work, a compass doesnt always point due north . With notable exceptions of course, such as heavy iron or other ferrus metal deposits in an area which can seriously affect the reliability of a compass.

Map Number & Print date

Relevant only in the way that an expiry date is relevent on food, very. If the print date is a long time ago, while the general landscape may not have changed, paths and river locations as well as drinkable water sources may have varied significantly. Planning a hike with an older map is fine, and using the map on a walk is fine too, just be aware that geo-spacial data is subject to change and because of shifting magnetic fields around earth magnetic declination in an area can change significantly in as little as 10 years. When taking survival and navigation into consideration $10 it takes to buy a new map might well be worth the effort.

Trail info / suggesting trails

Many maps come with several suggested trails, some even going to the level of detail that shows elevation profiles, water stops and all the scenic excitement you can find. They can also be very helpful for noting logging truck trails, trails shared with motorbikes and other vehicles.

Distinct features

Why do we go walking? Most people go to see something, or conquer a mountain, either way, these kind of distinct features are readily depicted on most maps.

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