Map Abstraction and Generalization

Map Abstraction

• Map abstraction is the process of moving from the "real world" to the world of maps
• Map content and shape vary according to purpose, need, and resources
• Map generalization is the process of reducing the amount of detail in a map or database in a meaningful way
• Generalization examples:
  • Topographic map 1:10,000 vs. 1:50,000
  • The relation between scale and generalization: as scale decreases, detail increases, and as scale increases, area decreases
  • Scale 1:10,000 = 1 cm = 100 meters, Scale 1:50,000 = 1 cm = 500 meters, etc.

Map Anatomy

• Map scale:
  • Ratio of the distance on a map to the actual distance on the ground
  • Example: 25,000:1, where 1 cm on a map is 25,000 cm in real life
• Types of map scales:
  • Bar scale (visual guide)
  • Lexical scale (gives distance conversion in words)

Coordinate Systems

• Coordinate systems:
  • A set of numbers used to determine position on the surface of the earth
  • Geographic coordinate system (GCS) uses latitude and longitude to specify locations
• GCS parts:
  • Latitude: defines how far north or south a point is on the globe relative to the equator (0° to 90°)
  • Longitude: defines how far east or west a point is on the globe relative to the prime meridian (0° to 180°)

Map Projections

• Map projections:
  • Methods and procedures used to transform the spherical 3D earth into 2D planar surfaces (e.g., paper maps, computer monitors)
  • Mathematical formulas used to translate latitude and longitude on the earth to x and y coordinates on a plane
• Map projection surfaces:
  • Plane surface
  • Cone surface
  • Cylinder surface

GIS Project

• GIS project phases:
  • Collect data from different sources (paper map, satellite, etc.)
  • Create geo-database
  • Geo-reference
  • Digitization
  • Attribute data
  • Typology
  • Analysis
  • Typo-graph

Map Abstraction (continued)

• Layers in GIS:
  • Two types of data: raster and vector
  • Raster: organized as cells arranged in rows and columns
  • Vector: uses points, lines, and polygons
• Data layers in GIS:
  • Represent data in layers

What is Map Anatomy?

• Map anatomy:
  • The study of the structure and components of maps
  • Objectives: to understand maps, map types, map scale, coordinate systems, and map projections
• Maps and map types:
  • Maps can be stored in our brain (mental maps)
  • Maps can be printed on paper
  • Maps can appear online
• Map types:
  • Three types: reference maps, thematic maps, and others