Isoline Maps - Introduction to Geography - Geography for Kids
Starting at the highest elevation, draw straight lines to the nearest neighboring Related to this element of subjectivity is the fact that the fidelity of a contour map First, view an image of an irregular array of 16 spot elevations. Related Links . Find contour lines Stock Images in HD and millions of other royalty-free stock photos, illustrations, and vectors in the Shutterstock collection. Thousands of new . An image of a topographical map made with isolines. An example of a Contour lines show places that have the same height on land. Isohyets are isolines that.
Isallobars are lines joining points of equal pressure change during a specific time interval. An isopycnal is a line of constant density.
An isoheight or isohypse is a line of constant geopotential height on a constant pressure surface chart. Isohypse and isoheight are simply known as lines showing equal pressure on a map.
Therefore, all points through which an isotherm passes have the same or equal temperatures at the time indicated. The term was coined by the Prussian geographer and naturalist Alexander von Humboldt, who as part of his research into the geographical distribution of plants published the first map of isotherms in Paris, in An isocheim is a line of equal mean winter temperature, and an isothere is a line of equal mean summer temperature. A map with isohyets is called an isohyetal map.
An isoneph is a line indicating equal cloud cover.
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- Topographic Maps (Topo Maps) and Contour Lines
An isochalaz is a line of constant frequency of hail storms, and an isobront is a line drawn through geographical points at which a given phase of thunderstorm activity occurred simultaneously.
Snow cover is frequently shown as a contour-line map. In meteorology, the term isogon refers to a line of constant wind direction. Freeze and thaw[ edit ] An isopectic line denotes equal dates of ice formation each winter, and an isotac denotes equal dates of thawing. Physical geography and oceanography[ edit ] Elevation and depth[ edit ] Topographic map of StoweVermont.
The brown contour lines represent the elevation. The contour interval is 20 feet. Contours are one of several common methods used to denote elevation or altitude and depth on maps.
From these contours, a sense of the general terrain can be determined. They are used at a variety of scales, from large-scale engineering drawings and architectural plans, through topographic maps and bathymetric chartsup to continental-scale maps.
In cartography, the contour interval is the elevation difference between adjacent contour lines. The contour interval should be the same over a single map.
When calculated as a ratio against the map scale, a sense of the hilliness of the terrain can be derived. Interpretation[ edit ] There are several rules to note when interpreting terrain contour lines: The rule of Vs: This is a consequence of erosion. The rule of Os: If a loop instead represents a depression, some maps note this by short lines radiating from the inside of the loop, called "hachures".
Two or more contour lines merging indicates a cliff. By counting the number of contours that cross a segment of a streamthe stream gradient can be approximated. Of course, to determine differences in elevation between two points, the contour interval, or distance in altitude between two adjacent contour lines, must be known, and this is normally stated in the map key.
Usually contour intervals are consistent throughout a map, but there are exceptions.
Topographic Maps (Topo Maps) and Contour Lines Introduction
Sometimes intermediate contours are present in flatter areas; these can be dashed or dotted lines at half the noted contour interval.
When contours are used with hypsometric tints on a small-scale map that includes mountains and flatter low-lying areas, it is common to have smaller intervals at lower elevations so that detail is shown in all areas. Conversely, for an island which consists of a plateau surrounded by steep cliffs, it is possible to use smaller intervals as the height increases.Labeling contour lines in ArcGIS
The term equipotential line or isopotential line refers to a curve of constant electric potential. Whether crossing an equipotential line represents ascending or descending the potential is inferred from the labels on the charges. In three dimensions, equipotential surfaces may be depicted with a two dimensional cross-section, showing equipotential lines at the intersection of the surfaces and the cross-section.
The general mathematical term level set is often used to describe the full collection of points having a particular potential, especially in higher dimensional space. Magnetism[ edit ] Isogonic lines for the year The agonic lines are thicker and labeled with "0". In the study of the Earth's magnetic fieldthe term isogon or isogonic line refers to a line of constant magnetic declinationthe variation of magnetic north from geographic north.
An agonic line is drawn through points of zero magnetic declination. An isoporic line refers to a line of constant annual variation of magnetic declination. Oceanography[ edit ] Besides ocean depth, oceanographers use contour to describe diffuse variable phenomena much as meteorologists do with atmospheric phenomena.
In particular, isobathytherms are lines showing depths of water with equal temperature, isohalines show lines of equal ocean salinity, and Isopycnals are surfaces of equal water density. Such lines are called index contour lines. They are usually labeled with their corresponding elevations.
Contour lines thinner lines between index contours are called intermediate contour lines. In the map shown below, the elevation difference between index lines is meters.
The elevation difference or vertical distance between two adjacent contour lines would be 20 meters Therefore the contour interval is 20 meters. In some situations the elevation and terrain relief can not be shown with enough detail using index and intermediate contours using the standard contour interval. This is more often seen in very flat areas with minimal change in elevation where the spacing between contour lines becomes very wide. In such cases, supplementary contour lines in the form of dashed lines are used to provide more information about the topography and help in detecting small changes in elevation.
The contour interval for supplementary contours in usually half the regular contour interval. For example in the above case where the contour interval is 20m, the distance between a supplementary contour line to the closest contour would be 10m. Typically the interval used for supplementary contours is noted next to the regular contour interval in the map legend. Hachured contour lines are another form of contours used to depict terrain depression, and are explained in a future section.
How to read topographic maps Reading topographic maps entails estimation of the elevation of desired locations on the map as well as acquiring a feel for the three dimensional relief, and shape and location of the terrain features. Labeled contour lines along with the contour interval can be used to derive the elevation of a location.
To find the elevation of point A we can start from a labeled line and count the number of intermediate lines to get to the point or near the point. Starting from the m line moving right toward point A there is a loss of elevation, since we are moving toward m elevation.
The first contour adjacent to m is 20m lower i. Therefore point A sits at m. Alternatively we can start from m and add 20m for every contour until we reach point A. There are 3 contours with each having 20m elevation change.
Point B is located between two contour lines, therefore its elevation is somewhere between the elevations of the sorrounding lines.
Moving right from the m line the elevation decreases, the elevation of Point B can be estimated as around m between m and m. In many cases moving across the map the same elevations are encountered more than once. Such scenarios can happen for example when moving up the slope of a mountain to a ridge line or a pass and coming down the other side, or traveling across a valley bottom.
In this image point A is clearly located on the bottom of a valley south of the lake. Carefully looking on both sides of the point we can locate the m labeled contours. There are no other contours on the valley bottom below m the next contour lower than m would be mtherefore the valley bottom should be between m and m elevation.
Point A's elevation can be approximated to be somewhere in s meter range. Looking north of the lake we can see the elevation gradually decreasing as the river originating from the lake moves downstream. The next contour line m is located just north of the lake. Climbing up from the valley toward west left of the map elevation of m is reached.
Considering the shape of the terrain, there seems to be a broad ridge to the south of m peak indicated with spot elevationpoint C lies on a small pass or col and point B is located on a ridge or broad peak south of the pass. It is clear that by traveling from east to west elevation has increased, and after the pass the elevation drops back down to m and possibly lowers more on the west side of the mountain. Looking at m contour on both sides, elevation of the intermidiary contours are found conveniently.
Point B is sorrounded by the m contour line. There is no other contour line above this line next one would be m elevationtherefore point B should be somewhere between m and m elevation.