Understanding Map Symbols: Scale, Contours, and Climograms
Understanding Map Symbols
Scale
The scale is the mathematical relationship between real-world dimensions and their representation on a map or plan. For example, a scale of 1/500 indicates the relationship between the graphic size (on paper) and the actual dimensions on the ground.
Contour Lines
A contour line connects points of equal elevation on a map. Contour lines are often printed in sienna for land features and blue for glaciers, deep sea areas, and lakes. A contour line (also called an isopleth, isoline, contour, or isarithm) represents a curve connecting points where a function has the same constant value.
Isolines are lines or curves on a map that describe the intersection of a real or hypothetical surface with one or more horizontal planes. The configuration of these curves allows map readers to infer the relative gradient of a variable or parameter and estimate its value at a given location.
Isotherms
An isotherm is a curve connecting points on a map that have the same temperature at a specific time. Multiple isotherm maps can be created for the same area, showing, for example, average temperatures for January, February, or mean annual temperatures.
Isobars
An isobar is an isoline of pressure, representing a line of equal or constant pressure on a graph or map. Isobars typically connect points of equal atmospheric pressure.
Isohypses
Isohypses are lines connecting points of equal height or altitude.
While temperatures may be low, they are not necessarily in the -5°C to -30°C range. Clouds dissipate as air moves down a slope, causing the temperature to rise and humidity to decrease.
Contour Features
Contour features exhibit the following characteristics:
- Contours do not cross each other.
- They form closed lines, although this may not be apparent within the map’s boundaries.
- Closer spacing indicates a steeper slope, while wider spacing indicates a gentler slope.
- The direction of maximum slope is at right angles to the contour.
- They are closed lines with a regular and uniform stroke.
- They tend to be parallel, especially in wide valleys.
- They form a “U” shape with the convexity pointing towards lower ground or on flat curves of crests.
- They form a “V” shape with the apex pointing upward in drainage areas.
- They may form an “M” shape at the junction of two crests.
- Except in steep reliefs, they never touch or merge.
- They never bifurcate.
- The equidistance between curves has a constant absolute value but depends on the map scale, the importance of the relief, and the precision of the survey.
Curvimeters
Curvimeters are measurement tools, both analog (mechanical) and digital, used to accurately measure the distance or length between two points on a map or plan, even without considering elevation changes.
Climograms
A climogram is a graphic representation, often a double-entry chart, summarizing precipitation and temperature data collected at a weather station. Average data for each month of the year are presented, considering precipitation and temperature averaged over the observed years.
Climograms have a horizontal axis representing the months of the year, a vertical axis on the right (usually) representing the temperature scale, and a vertical axis on the left representing the rainfall scale.