What is Contour (Contour Lines)? - What it means?

Contour lines are closed curves that are formed by joining the points that have the same altitude value, starting from sea level on the earth. The sea level is considered to be 0 meters and is the initial level of the contour. The values ​​increase according to the altitude from sea level.

What is Contour Method?

Contour method is a method of showing landforms with contour lines.

Contour may seem complicated at first glance. These curves are actually lines that make sense when they come together and enable us to show and recognize the landforms. Contour method still maintains its role as one of the most preferred methods for displaying landforms.

In this method, isohips curves are drawn according to a certain elevation range. For example; If there is a difference in elevation of 10 meters between two contours, this value is also preserved between the other contours. We can state that for this scenario, all contour on the map were created at intervals of 10 meters. Contour curves in contour maps are divided into two groups as main and intermediate curves. The darker and thicker curves are the main contour, while the lighter and thinner curves are intermediate contour. This makes it easier to read contour maps.


Contour Lines and Properties

The general features of the contours, which give information about the forms and heights of the landforms, are as follows:

  • — Contour do not cross each other in any way.
  • — Shows the landforms with their elevations.
  • — It is created with equal elevation intervals.
  • — The elevation difference between two successive contour is equal in the whole study area.
  • — All points where a contour line crosses have the same elevation value.
  • — Zero (0) meters denotes the contour of the shoreline.
  • — The slope increases in the areas where the curves are dense, and the slope decreases in the areas where the curves are sparse.
  • — Two adjacent contour lines that do not cover each other have the same elevation.

How is Contour Calculation Made?

Various calculations can be made using contour maps. Slope and elevation calculations are the most commonly needed calculations. In addition to these calculations, bird flight distance calculation can also be made on contour maps, as in every map. When calculating slope or elevation, first of all, it is necessary to know the contour values ​​and to have the information of the elevation between the contour. For example; If the elevation value of one of the contour is known and there is information about how many meters it was created at intervals, the height calculation of the desired place can be made. The elevation of the desired place can be found by counting the contours by using the elevation difference between the two contour. The product of the number of contour spacing by the difference in elevation between two contour represents the total elevation.

After the altitude information is determined, slope calculation can be made between two points in percent (%) or thousandths (‰). The following formula is used to calculate the slope:

How to Find the Elevation Difference Between Contour?

The difference in elevation between two contour is called equidistant (range of contour). The elevation difference between contours can be found by subtracting the smaller value from the larger value from the two consecutive contourin values. Contour are drawn with equal elevation intervals. For this reason, when the elevation difference of two consecutive contour intertwined in any area is determined, this difference is the same in the whole map. For example; If the elevation value of the contour drawn after the 0 meter contour at the seaside is 20 meters, the elevation difference between the two contour is 20 meters. Since the elevation difference will be constant between the contour, the third contour to be drawn will have a value of 40 meters.

Contour Map Landforms

The most common use of contour maps is to show landforms. Even today, one of the methods that can easily show the landforms is the contour method. The frequency and sparsity of the curves in these maps express the landforms and features.

Mountain, peak, valley, plateau, ridge, neck, pit (bowl), estuary, delta, coastline, waterfall and cliff (cliff) shapes can be shown on contour maps. In addition to these landforms, places where the slope of the earth is less or more can be extracted from contour maps. Areas where the curves are sparse indicate that the slope is low, and the areas where the curves are tight indicate that the slope is high.

Contour Pass, Valley, Chine, Delta and Cliff

Let us briefly examine some of the landforms illustrated by the contours mentioned in the previous chapter:

Pass: It is the low area between two opposite hills.

Valley: These are the areas shown as “˄” (inverted V) of the contour lines towards the direction where the elevation values ​​increase. The valleys are formed as a result of river erosion and the valley is also included in the contour maps with the rivers.

Chine: It is the slopes where the contours fold in the form of “V” in the direction of decreasing the altitude values ​​on any hill.

Delta: These are the projections that occur in the form of a triangle towards the sea side. In general, deltas are formed by the accumulation of alluvium in the place where the rivers reach the sea.

Cliff: It is the name given to the steep sloped coasts. The very frequent presence of curves near the sea in an contour map indicates the presence of a cliff.

Creating an Contour Map

Contour maps are maps that usually show landforms, prepared using contour as a bird’s eye view. This type of map is also called topographic map. As in all types of maps, such maps must have a title suitable for the purpose of the map, a scale bar that expresses the scale of the map, direction arrow, legend, parallel and meridian map elements.

In order to prepare an contour map, it is necessary to have contour data belonging to the study area in question. Contour can be created by hand drawing manually with the traditional method, or they can be created automatically in a shorter time and faster through Geographic Information Systems (GIS) programs. With MapInfo Pro, one of the GIS programs, using digital terrain model data, contour can be created automatically according to desired elevation ranges. The process of creating contour in the MapInfo Pro program is explained in detail in the video below.

Colorful Contour Map

Contour maps can be prepared in black and white as well as in color.

In the drawings made manually with the traditional method, black and its tones were generally preferred to create contour.

With the introduction of geographic information systems into our lives, colored contour maps have started to be preferred more. While giving color to the contour, they are usually defined by determining the colors according to their height values.

Turkey Contour Map

While contour maps can be created for local regions such as neighborhoods, they can also be created on the basis of district, province and even country. The contours can be read more easily in small regions, it is difficult to read and understand the map in large areas such as the country. For this reason, the size of the study area and the elevation difference of contour should be determined according to the need. For example; When it is desired to prepare a Turkey Contour Map, the altitude between the contour should be different. When contours are created at 50 meters intervals for the whole of Turkey, the curves will be too much, so the readability of the map will decrease and its intelligibility will decrease.

World Contour Map

The subject mentioned in the previous topic is also valid for the World Contour Map. When it is desired to create a contour map around the world, the elevation difference between contour lines should be determined high. While preparing both Turkey Contour Map and World Contour Map, it is necessary to have contour data covering the whole area. Manually drawing such a large area by hand will not be possible. For this, contour can be created automatically by using digital terrain model data through MapInfo Pro program, one of the geographic information systems programs. The processing time varies according to the size of the working area and the data used.