What Is The Index Contour Line?

What do contour lines mean?

Contour line, a line on a map representing an imaginary line on the land surface, all points of which are at the same elevation above a datum plane, usually mean sea level.

map: contour lines.

The diagram illustrates how contour lines show relief by joining points of equal elevation..

Which of the following is the best definition for contour line?

Rules of Contour Lines In other words, contour lines connect points of equal elevation. By definition, contour lines separate points of higher elevation from points of lower elevation. This means it is always possible to define an “uphill” direction on one side of a contour and a “downhill” direction on the other side.

What is the elevation difference between contour lines?

The elevation difference between two adjacent contour lines is called the contour interval (CI). Usually the contour interval is noted on the map legend. In most topographic maps every 5th contour line is drawn in bold print or wider than other contours. Such lines are called index contour lines.

What is the distance between contour lines?

A contour line is a line drawn on a topographic map to indicate ground elevation or depression. A contour interval is the vertical distance or difference in elevation between contour lines. Index contours are bold or thicker lines that appear at every fifth contour line.

How do you find the index contour?

On most maps, each fifth contour line, shown as a heavier or darker line, is an index line or index contour. These index lines will be marked with their elevation. Find the elevations of two adjacent index lines. The highest number shows the uphill rise.

What is a supplementary contour line?

Supplementary contour lines are placed between regular contour lines to visualize small but important forms that regular contour lines are unable to show. On topographic maps, typical forms are hillcrests, depressions, saddles, terraces, banks, and levees.

How do you read contour lines on a site plan?

Closely spaced contour lines indicate steep slope. Widely spaced contour lines indicate gentle slope. Equally spaced contour lines indicate uniform slope. Closed contour lines with higher elevation towards the centre indicate hills.

How do you contour a survey?

In this method, the contours to be located are directly traced out in the ground by locating and making a number of points on each contour. These points are then surveyed and plotted on plan and the contours drawn through them.

Why can’t contour lines cross?

Contour lines can never cross one another. Each line represents a separate elevation, and you can’t have two different elevations at the same point. … Moving from one contour line to another always indicates a change in elevation.

What is contour curve?

A contour line (also isoline, isopleth, or isarithm) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a plane section of the three-dimensional graph of the function f(x, y) parallel to the (x, y)-plane.

What are 3 types of contour lines?

There are 3 kinds of contour lines you’ll see on a map: intermediate, index, and supplementary.Index lines are the thickest contour lines and are usually labeled with a number at one point along the line. … Intermediate lines are the thinner, more common, lines between the index lines.More items…

What is the space between contour lines called?

The space between the contour lines is called the contour interval and represents a specific (set) distance. If the contour interval is 50 feet, the vertical space between the two contour lines is 50 feet.

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.

How do you read a plot plan?

Tips on How to Read a Site PlanFind The Title Block. In the bottom right corner of most plans, you’ll find what’s called a title block. … Learn the Plan’s Scale. … Determine the Orientation of the Plan. … Know the Datum Point. … Note the Site’s Contours. … Locate Existing Structures.

What are the characteristics of contour lines?

Other characteristics of contour lines are: – Uniform slopes have uniformly spaced lines. – Along plane surfaces, contour lines are straight and parallel. – Contour lines are perpendicular to lines of steepest slopes. – For summits or depressions, contour lines most close upon themselves.