Map Symbols, Scale, and Distance/Direction

Map Generalization

Types of Symbols

• Line Symbols: Represent real-life objects with a linear path.
• Point Symbols: Represent objects occurring at a single point on Earth's surface using a dot.
• Area (Polygon) Symbols: Represent real-life objects spread over Earth's surface using geometric shapes.

Generalization Techniques

Reality contains too much information for a single 2D map. Generalized geometry and content make a map useful. A good map suppresses less important information to highlight what needs to be seen.

• Selection: Only relevant line, point, and area features are chosen.
• Classification: Grouping similar features and using a common symbol to represent them.
• Simplification: Reduction of unnecessary detail.
• Smoothing: Smoothing out abruptly joined lines.
• Enhancement: Giving map symbols more realistic appearances.

Scale

Scale is a ratio comparing the relationship of features on a map to their actual size. It can be represented as a graphic, linear, or bar scale.

• Large Scale: Shows a smaller area in considerable detail with less generalization.
• Small Scale: Shows a larger area with little detail and more generalization.

Distance and Direction

Distance

• Absolute Distance: Spatial separation between two places on Earth's surface measured by a standard unit (e.g., miles, kilometers).
• Relative Distance: Converts linear measurements into something meaningful to the individual, not necessarily using standard units (e.g., "I live 30 minutes from work").

Direction

• Absolute Direction: A quantitative concept using standard compass bearings (e.g., "The ship's heading is N25E").
• Relative Direction: A qualitative concept (e.g., "I live in northeast Ohio").
• True North: The northerly direction along a line of longitude (meridian). Meridians converge near the poles.
• Magnetic North: The direction a compass needle points, aligning with Earth's magnetic lines of force, not the North Pole.
• Magnetic Declination: The deviation of Earth's magnetic field from true north.
• Grid North: The direction of north-trending grid lines for special grids (e.g., state plane, UTM, or local grids). Grid lines, unlike meridians, do not converge, which can result in inaccuracies outside the map's central area.