Cartographic Elements and Meteorological Concepts
Cartographic Scale
Scale is the mathematical relationship between real-world dimensions and their representation on a map or plan. It defines the relationship between the graphic size (on paper) and the actual dimensions on the ground, for example, 1:500.
Contour Lines and Isolines
A contour line connects all points on a map having equal status, height, or elevation. Contours are typically printed in sienna for land maps and blue for glaciers, deep sea, and lake areas.
An isoline (also known as an isopleth, contour, or isarithm) for a function of several variables is a curve connecting points where the function has the same constant value. Isolines represented on a map are lines or curves 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 the variable or parameter and estimate a value at a given location.
Isotherm: Equal Temperature Lines
An isotherm is a curve connecting points on a map that have the same temperature during a specified time unit. For a given area, numerous isotherm maps can be created, such as average temperature isotherms for individual months (e.g., January, February) or mean annual temperatures.
Isobar: Equal Pressure Lines
An isobar is an isoline of pressure; that is, a line of equal or constant pressure on a graph or map. Generally, isobars connect points of equal atmospheric pressure on a map.
Isohypses: Equal Height Lines
Isohypses are lines connecting points of equal height or altitude.
Regarding atmospheric conditions, while temperatures can be low (e.g., -5°C to -30°C), clouds may dissipate as air moves down a slope. This downward movement causes the air temperature to rise and humidity to decrease, leading to cloud dissipation.
Characteristics of Contour Lines
Contour lines exhibit the following features:
- Contours do not cross each other.
- They must be closed lines, even if not entirely within the map’s boundaries.
- When contours are close together, they indicate a steeper slope; when they are far apart, they indicate a gentler slope.
- The direction of maximum slope is at right angles to the contour line.
- They are closed lines with a regular and uniform stroke.
- They tend to be parallel to each other, especially in wide valleys.
- They form a “U” shape with the convexity pointing towards lower ground or flat crests.
- They form a “V” shape with the apex pointing upstream in drainage areas.
- They present an “M” shape at the union of two crests.
- Except in very steep reliefs, they never touch or merge.
- They never bifurcate (split).
- The equidistance (vertical interval) between curves has an absolute value that remains constant for a given map; however, it depends on the map scale, the significance of the relief, and the precision of the survey.
Curvimeters: Measuring Distances on Maps
Curvimeters are measurement devices—available in analog (mechanical) and digital forms—designed to accurately measure the distance or length between two points on a map or plan, even without accounting for elevation changes.
Area Measurement on Maps
Tools are utilized to approximately measure the area of a region represented on a map.
Climograms: Climate Data Visualization
A climogram is a double-entry graphic that summarizes precipitation and temperature values collected at a weather station. Average data are presented for each month of the year, considering precipitation and temperature averaged over all observed years. Climograms typically feature:
- A horizontal axis for the months of the year.
- A vertical axis on the right (usually) for the temperature scale.
- A vertical axis on the left for the rainfall scale.