How to Read River Flow on Topographic Map
Which trail would you take?
Imagine. Yous're out mountain climbing with your friends.
You pull out your map and see ii hiking trails.
The first route has closely-spaced contour lines.
Only the second route has widely-spaced spaced contour lines.
Which hiking trail would YOU take?
For the slow-and-steady climber, you'd pick the 2nd road because widely-spaced contour lines mean the slope is gradual. Merely if yous picked the showtime road, you're the type of free climber who scales mountains with only a pickaxe. This is because when contours are close together, it ways that the gradient is steeper.
For a quick definition, a contour line joins points of equal and abiding values. For example, contours on an acme take constant heights that are the same on each line in a topographic map.
Are these contour lines mountains or depressions?
When you have a closed profile like the one below, this means there is a hill/mountain or depression.
You don't really know unless there is a characterization on the contour line. In the case beneath, nosotros've added labels and it should be articulate that information technology'due south a depression.
And this isn't but any low. This is the massive meteor crater that struck Arizona a long fourth dimension ago.
On some maps, cartographers apply teeth marks or hachures for depressions at craters or volcanoes because information technology marks the elevation goes up or downward.
READ MORE: A Topographic Profile of Arizona's Massive Meteor Crater
How does Mountain Fuji's profile lines look like?
In this case, closed contour lines bespeak a mountain. The beautiful Mountain Fuji stands iii,776 meters tall higher up sea level. At 250-meter spacing, here's how the contour lines wait:
When you see Mount Fuji in 3D, yous can run across that it'due south quite steep every bit the contours are relatively closely spaced together.
So far, we've seen examples of 2 types of closed contours, but how practice contours expect like in valleys?
The rule of V and U-shaped valleys
Valleys are elongated low-lying depressions commonly with a river flowing through it. Yous know that you lot're looking at a valley bottom when contour lines are V or U-shaped.
Here is an example of a 3D view of the picturesque Collayomi Valley in California:
All rivers flow downhill from higher to the lower elevations, perpendicular to the contour line above it. As a dominion of thumb, the V-shaped contour is pointing upstream (the opposite direction from the flow of a stream or river).
The "V" shape contours indicate streams and drainage. Equally you lot tin can see, the "V" points uphill to a college pinnacle. Generally, you lot can connect the apexes of the upwards-pointing, "5" shaped contour lines to delineate a stream. Further to this, you can estimate a stream gradient by counting the number of contours that cross a stream with the contour interval.
The slope is always perpendicular to contour lines. The less separation between profile lines means a steeper gradient and vice versa. When there are evenly spaced contours, the slope is uniform.
At a stream junction, contour lines class a "One thousand" or "West" shape. This can be interpreted as 2 "5-shaped contours intersecting.
What near ridges and gullies?
Over time, gullies form through erosion of running water on hillsides. A consequence of ii eroded gullies is a spur at the centre on the face of a hillside that sticks out. Both gullies and spurs run from ridgelines to valley bottoms.
Gullies (or draws) are characterized past "U" or "5" shaped contour lines with their closed-terminate pointing towards higher top. On the other hand, spur contour lines point toward lower elevation.
In second, these valley landscape features are a bit more than hard to see. Simply it's key to call back how ridges bespeak downslope and gullies point upslope.
Why do contour lines never cross?
It's unlikely that contours cantankerous, but sometimes they practice. When the terrain is an overhang or cliff, profile lines volition cross or touch.
The cliffs in Látrabjarg, Iceland are up to 440 meters tall. When you generate 100-meter contours, they are very close to converging.
In 3D, you can come across how steep these cliffs are. So if these contours did cross, it'southward very likely an overhang. Or it could be an error in the program.
If y'all apply your imagination, picture show an overhang where the terrain hangs outward. This would be a rare exception when two contours that cantankerous.
How to describe contour lines manually?
You can easily generate profile lines with the click of a button in CAD or GIS software. Only what if yous want to describe it past hand?
Outset, y'all accept to cull a contour interval. For case, we're going to employ a contour interval of 10 meters. So this means that in that location will exist a profile every 10 meters.
Between transition points of ten (thirty, 40, 50, etc), add markers where to draw lines. Basically, draw or interpolate between the lines.
Now that we take points to connect, allow's draw smooth contour lines for each interval. Substantially, we are connecting the points with lines.
And there we have it.
What do nosotros apply contour lines for?
In our example, contour lines represented constant superlative and showed the topography of the mural.
But meteorology (isopleth), magnetism (isogon) and even drive-time (isochrones) also utilize contours for different purposes.
The closeness of contours indicates slope. Irregular contours mean rugged terrain. It'south rare in nature for contours to cross. But they can for overhangs and cliffs.
What are some other types of contours y'all've seen in nature?
References
Topographic Maps: The Basics, Natural Resources Canada, 2020. Reproduced with the permission of the Department of Natural Resource, 2020.
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Source: https://gisgeography.com/contour-lines-topographic-map/
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