Index contours are
bold or thicker lines that appear at every fifth contour line
. If the numbers associated with specific contour lines are increasing, the elevation of the terrain is also increasing.
What is an index contour and why are they important?
To make topographic maps easier to read, every fifth contour line is an index contour. Because
it’s impractical to mark the elevation of every contour line on the map
, the index contour lines are the only ones labeled. The index contours are a darker or wider brown line in comparison to the regular contour lines.
How do you find the index contour?
Divide the difference in elevation between the index lines by the number of contour lines from one index line to the next
. In the example above, the distance 200 is divided by the number of lines, 5. The contour interval is equal to 200 / 5 = 40, or 40-unit contour intervals.
What is a contour index line and how do you know it is a contour index line?
1. Index lines are
the thickest contour lines
and are usually labeled with a number at one point along the line. This tells you the elevation above sea level.
What are index contours marked with?
A contour line shown on a map in a distinctive manner for ease of identification, being printed more heavily than other contour lines and generally labeled with
a value (such as figure of elevation) along
its course.
What are 3 types of contour lines?
Contour lines are of three different kinds. They are
the Index lines, Intermediate lines and the Supplementary lines
.
What are the methods of contouring?
- Direct Method of Contouring : High degree of precision is required for large-scale maps with small contour interval. …
- Indirect Method of Contouring : It is suitable for undulated ground and hilly areas.
What are Index contour lines for?
The index contours are a darker or wider line in comparison to the regular contour lines. Elevations are marked on the index contour lines only. To
determine the gradient of elevations
, observe the amount of space in between the lines. If the contours are placed close together, then you’re looking at a steep slope.
Why do contour lines never cross?
Contour lines never cross on a topographic map
because each line represents the same elevation level of the land
.
How do you study contour lines?
- The close together contours in the top left show a steep slope.
- The spaced out contours in the bottom left show a shallow slope.
- The upside down v-shape on the right is a small valley that also goes downhill from the top of the map to the bottom.
- There is a hill peak just over 430m at the top centre of the map.
What are the 5 Rules of contour lines?
Rule 1 – every point of a contour line has the same elevation. Rule 2 – contour lines separate uphill from downhill. Rule 3 – contour lines do not touch or cross each other except at a cliff. Rule 4 –
every 5th contour line is darker in color
.
Does Google Earth show contour lines?
This KML network link displays a map overlay for USGS Contours (http://viewer.nationalmap.gov/) in Google Earth. To get started, simply download usgs-contours-overlay-for-google-earth. Or checkout all 4 USGS The National Map map overlays on this site. …
How do you measure contour lines?
Lighter contour lines do not have elevations, but can be determined by
counting up or down from the nearest index contour line and multiplying by the contour interval
. The contour interval is stated on every topographic map and is usually located below the scale.
What is a contour line art?
A contour line
defines the outline of a form, as well as interior structure
, without the use of shading. A fundamental basis of drawing, contour lines are usually the first technique children adopt to draw people, houses, and trees.
How do contour lines work?
Contour lines
connect points that share the same elevation
: Where they’re close together (they never intersect), elevation is changing rapidly in short distance and the terrain is steep. Where contour lines are wide apart, elevation is changing slowly, indicating a gentle slope.
What are 4 types of contour lines?
- Isopleth. Isopleth on a contour map connects the places having the same value of some measurable quantity of geographical or meteorological phenomena. …
- Isohyet. …
- Isobar. …
- Isobath. …
- Isohaline. …
- Isotherm. …
- Isohel. …
- Isohume.
