What do the tick marks on closed contours indicate?

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In summary: Contours that represent depressions have tick marks on the downhill side. This is only true of closed contours.
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DaveC426913
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I'm trying to make a physical 3D map of this landscape.

These isolated curves (red) have no altitude on them, so it's up to me to interpret.

How do I know if these are hills or dips?

Can I gather from the rising landscape (marked in magenta) that these are probably hills?
Can I be sure?
test.png
 
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  • #2
Huh. I don't see how you COULD know. It certainly seems likely that they are above the surrounding territory, but that's not a given. It would be perfectly correct to draw the landscape that way if they were dips.
 
  • #3
Google Earth or Map? Usually you can just "feel" it from the contours. Interesting.
 
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  • #5
hutchphd said:
According to this source
http://geokov.com/Education/mountain-pass-cliff.aspxIf it is a depression it should have tick marks on the low side. I do remember seeing these on charts. The mountains have no tick marks.
Those cartographers are careful folks.
Interesting. What kind of tick marks? Can you show an example?
 
  • #7
phinds said:
Interesting. What kind of tick marks? Can you show an example?
It's at the bottom of the page on his link.
 
  • #8
But I don't think depth charts use the tick marks for bottom contours. It would probably make them too "busy" but I don't know that they differentiate them. They are color coded for shallows so its usually easy to tell.
Anybody know?
 
  • #9
hutchphd said:
According to this source
http://geokov.com/Education/mountain-pass-cliff.aspxIf it is a depression it should have tick marks on the low side. I do remember seeing these on charts. The mountains have no tick marks.
Those cartographers are careful folks.
Thank the heck out of you! Of course!

(Alas, these are digital maps from Toporama. I'm not sure if they're actually showing that symbol. And it's very difficult to verify.)Now that I think about it, depressions are a comparatively rare artifact - especially if not water-filled or at least marshy. 99.9% of small, closed-contour land features are going to be bumps.
 
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  • #10
In the top left is a gully, cut into a scarp. It feeds an alluvial fan at the foot of the scarp, that fan has a gentle slope and covers the local bedrock. In the lower right, the distinctive lack of chevron patterns made by streams in valleys, makes it look like a karst landscape. I would expect sinkholes with such a geology, but those isolated and closed contours appear to be on steadily sloping ground, which suggests they are more likely to be raised limestone spires = hills.
I wonder, what is the local rainfall?
 
  • #11
From this map, it appears to be treated the same way.
hutchphd said:
But I don't think depth charts use the tick marks for bottom contours. It would probably make them too "busy" but I don't know that they differentiate them. They are color coded for shallows so its usually easy to tell.
Anybody know?
I checked a chart online and it appears that depressions in the local topography are treated the same underwater. It's been a while since I did any cartography but think about it this way. If there was no water, where would you start creating tick marks? Certainly not at the 'shoreline' that doesn't exist.

https://www.mindat.org/glossary/depression_contour
A closed contour, inside of which the ground or geologic structure is at a lower elevation than that outside, and distinguished on a map from other contour lines by hachures marked on the downslope or downdip side.
 
  • #12
A bit of clarifying colour banding helps clear it up.

test2.png


I'm glad I took the time to colour the whole thing. I would have been hopelessly lost pretty quickly if I hadn't.
 

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  • #13
Closed contours that represent depressions have tick marks on the downhill side. This is only true of closed contours. You can see such features on karst features such as sinkholes. Being a caver, I often peruse topo maps online for such features to find caves. You can find many such features on topo maps of N. Florida just south of Tallahassee where there are many sinks.
 
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DBO said:
Closed contours that represent depressions have tick marks on the downhill side. This is only true of closed contours.
Under what conditions are contours not closed? 😕
 
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1. How do you determine the contour interval on a map?

The contour interval on a map is determined by the scale of the map and the elevation range of the area being represented. Generally, the larger the scale of the map, the smaller the contour interval will be. The elevation range refers to the difference between the highest and lowest points on the map. To determine the contour interval, divide the elevation range by the number of contour lines desired.

2. What is the purpose of determining contours on a map?

The purpose of determining contours on a map is to show the shape and elevation of the land. Contour lines connect points of equal elevation, allowing viewers to visualize the topography of an area. This information is important for navigation, planning, and understanding the physical characteristics of a location.

3. How are contour lines created on a map?

Contour lines are created by connecting points of equal elevation on a map. These points are determined by using surveying equipment or satellite imagery to measure the elevation of the land. The contour lines are then drawn on the map, with each line representing a specific elevation.

4. What is the difference between index contours and intermediate contours?

Index contours are thicker and usually labeled with the elevation they represent. They are typically every fifth contour line and help the viewer quickly determine the elevation of the land. Intermediate contours are thinner lines that fall between the index contours and provide more detail about the shape of the land.

5. How do you interpret contour lines on a map?

To interpret contour lines on a map, it is important to understand that the closer the lines are together, the steeper the slope of the land. When contour lines are far apart, the slope is more gradual. Closed contour lines indicate a hill or peak, while open contour lines represent a depression or valley. Additionally, contour lines that cross a stream or river indicate a change in elevation, with the contour lines bending upstream.

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