How To Read a Topographic Map
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Table of Contents
What is a Topographic Map
Topographic maps were first introduced in the 1800s to understand the resource potential in search of minerals. It was a painstaking process where surveyors had to perform altitude measurements using aneroid barometers.
Calculations were done with steel tape measures and heavy equipment. It was then drawn on huge sheets of copper that was later reprinted into topographic maps. Now topography maps are still produced in a more efficient way using aerial photographs and satellite imaging. There are currently more than 56,000 topological maps of the United States.
Topographic maps are different from your average map. When looking down on a regular map, it is hard to identify the change in elevation of the ground. A terrain map helps humans remap a 3 dimensional world into a 2 dimensional representation of Earth’s landscape. A topo map gives you a better idea of the mountains, depressions or bodies of water.
If you are trying to get from point A to B, a regular road map can get you there. But if you strayed away from your backpacking trek, then you need an elevation map to help you safely navigate by identifying the terrains and contours of the land.
What Are Contour Lines
What does a topographic map show? The main feature is the contour lines. Contour lines show the steepness of a terrain. Contour lines that connect together within the same line means they are geographic points that share the same elevation.
When the lines are drawn close together, it means elevation is increasing rapidly. When the lines are further apart, it indicates a gentler slope. When the lines are very far apart, it shows the flat terrain.
The spacing between the lines is called the contour interval. If it uses a 5 feet contour interval, this means the elevation increases 5 feet for every line of elevation. You can find the contour level at the bottom of the map.
Smaller circles with thin spaced lines would mean there is a high mountain peak. A small circle with a tick marks a depression.
Usually every 5th contour line is thicker than other lines. This is called the index line where the exact elevation is listed. Contour maps are drawn to show the height of the ground above mean sea level (MSL).
The scale of the topographical map tells the details of the map. Example a larger scale map 1:100,000 vs a smaller scale map 1:10,000. It could mean 1 inch equals to 100,000 inches of the real world terrain. A smaller scale map will cover smaller areas with greater detail. If you want to see a larger area within the same sheet of map, with less details, then get a larger scale map. Generally most maps in the United States uses 1:24,000 scale, representing 1 inch to 24,000 inches on the ground.
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Colors and Symbols
Colors also help you visualize the terrain. Blue usually indicates streams or lakes. The streams may be represented by dash-dot or lighter weight lines if they are intermittent streams. Green suggests vegetation while light patches usually suggest open terrain.
Roads may be marked as private roads or public roads.
Symbols such as small dots may mean surface features, like sand or muddy areas. Buildings can be depicted as squares based on their actual shapes, while houses are shown as small black squares.
Grids are parallel lines that intersect at right angles to help you indicate precise positions. There are 2 types of referencing systems, UTM projection (Universal Transverse Mercator) using Easting or Northing. The 2nd is geographic, which uses degrees and minutes.
This grid system is commonly used in the military and survey purposes. It basically divides the surface of the earth into grids. At the top, a number is assigned to each grid, called the Zone number. At the bottom, a letter is assigned the right hand side, called the zone designator. So a location can be identified as 10 T.
Within the zone, there is a coordinate system that uses meters. A vertical position is defined as north, while a horizontal position is defined as east. An example is 401934 meters north.
Geographic (Latitude and Longtitude)
Latitudes measures north and south of the equator. The equator always starts with 0 degrees. As you go north, it will increase all the way to 90 degrees in the north. And if you go south, it will increase all the way to 90 degrees at the south.
Longitude measures the east and west of the Prime Meridian. Prime meridian is 0 degrees longitude. When you go all the way to the east of the meridian, it will increase up to 180 degrees to the east. While if you go all the way to the west of the prime meridian, it will increase up to 180 degrees to the west. Longtitude gets closer as it approaches the north and south poles.
To obtain a more precise location, 1 degree is divided to 60′ minutes. And for even more accuracy, you can calculate until the seconds.
You will usually find a symbol called magnetic declination, which is used for navigation with a compass. The true geographic north is represented by the center line with a star. This is the grid north line. The line next to it on the right represents the magnetic north, which matches your compass needle. This will indicate how much UTM grid and zone lines are offset from the true north.
Where to get Topo Maps
How to Utilize a Topographic Map for Outdoors
By knowing about the area’s terrain, it helps you plan the best way to hike up a peak or tackle the dense forest. You will know when to anticipate a steep slope ahead of you. If it is too steep, you know how to find an easier route around the mountain. It will make it easier to prepare in advance the amount of supplies in your backpack for your hike. In case of emergencies, you will know where get locate a water source or find a place to shelter in case of bad weather. Read here for the 10 survival gears to survive.
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