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An isopach map displays lines of equal thickness in a layer where the thicknesses are measured perpendicular to the layer boundaries. Isopach maps are also referred to as True Stratigraphic Thickness (TST) maps. [2] [3] An isochore map displays lines of equal thickness in a layer where the thicknesses are measured vertically.
Size, how much space a symbol occupies on a map, most commonly refers to the area of point symbols, and the thickness of line symbols, although the cartogram controls the size of area features proportional to a given variable. Size has been shown to be very effective at conveying quantitative data, and in the visual hierarchy.
A draw, sometimes known as a re-entrant in orienteering, is a terrain feature formed by two parallel ridges or spurs with low ground in between them. The area of low ground itself is the draw, and it is defined by the spurs surrounding it.
Terrain or relief is an essential aspect of physical geography, and as such its portrayal presents a central problem in cartographic design, and more recently geographic information systems and geovisualization.
The length and thickness of each stroke represents the drop in height along its direction: a short and thick stroke represents a short and steep slope, while a long and thin stroke represents a long and gentle slope. The strokes are spaced at an equal distance inside a row. The strokes have the same thickness inside a row.
The UK and Isle of Man have been extensively mapped by the British Geological Survey (BGS) since 1835; a separate Geological Survey of Northern Ireland (drawing on BGS staff) has operated since 1947. Two 1:625,000 scale maps cover the basic geology for the UK. More detailed sheets are available at scales of 1:250,000, 1:50,000 and 1:10,000.
A separate stylus is required for each thickness of line required. For example, a contour line might require a 0.15mm stylus whereas a major road might require a 0.5mm stylus. The scribe sheet is made of a stable plastic base material and coated with a material which is designed for easy removal using a scribing tool to produce a cleanly cut line.
Strabo, in his Geography (ca 20 AD), states that the maps in Eratosthenes's Geography Book 3 (3rd century BC, now lost) contained lines "drawn from west to east, parallel to the equatorial line" (thus the term parallel) [6] Ptolemy's Geography (ca 150 AD) gives detailed instructions for drawing the parallels and meridians for his two ...