Spatial Data

Spatial Data
- Mapping Process
  - purpose - communicating what to who
    - e.g.
      - roads for a tourist
      - roads for outdoor enthusiast
      - roads for emergency planning
    - topog.: detail set by Instructor
  - scale
    - limits level of detail (... generalization)
    - topog.: level of detail & page size
  - real world features
    - what is to be mapped
    - look back a purpose/ intent
    - topog.: elev. + planimetric (creek, road, trails) + thematic (forest)
  - map representation
    - how features are displayed
      - spatial entity type
        
        point, line, polygon (surface)
        
        scale (e.g. city at large vs small scale)
      - symbology
        
        point symbols
        
        line types
        
        size/ thickness of symbols/ lines
        
        colours
    - chloropleth (shading, colours)
    - topog.: points: spot hts; lines: creeks, roads; polygons: timber, swamps
  - generalization
    - factors
      - map scale
      - technology (thickness of line, size of pixel)
      - purpose of map
    - selection (ignored soils, and features less than 1/4 ha)
    - simplification (not much, scale was large)
    - displacement (not much, scale was large, no parallel features)
    - smoothing (contour lines)
    - combination (swamps?)
    - exaggeration (swamp width?)
  - map projection
    - topog.: no need, very large scale, actually you drafted a 'plan'
  - spatial referencing
    - topog.: relative to baselines
  - annotation
    - topog.: standards provided by Instructor
- Data (3 components)
  - time (when)
  - spatial (where, location)
    - discrete features
    - continuous phenomena
  - attribute (what, descriptive, "thematic")
- GeoReferencing
  - geographic: lat/ long
    - graticule
    - shape of the earth
    - need for datums
  - cartesian: UTM projection
  - datum - needs to be the same in GIS
- Projections
  - distortion
    - area, shape, distance, direction
    - scale varies on a map (by lots to very little)
  - map projections in BC
    - UTM
      - but zones are only 6 degrees - 5 zones in BC
      - cannot use UTM for a single map of BC
      - distortion:
        
        distance: 0.04% (or 4cm in 100m)
        
        area: 0.08% (or 8m2 in 1 ha)
    - BC Albers Equal Area
      - conic, tangent (stds: 50.0 & 58.5)
      - provides seamless coverage for BC
      - distortion:
        
        distance: 0.36% (or 36cm in 100m)
        
        area: 0 (remember it's "equal area")
- Spatial Entities
  - Points
    - 0 dimension i.e. a single coordinate
    - features too small to be represented by area
    - point vs polygon is scale dependent
    - e.g. lookout tower, log landing, city?
  - Lines/ Networks
    - 1 dimension, i.e. a string of connected points
    - linear features: roads, streams
  - Areas or Polygons
    - 2 dimensions, i.e. a closed string of coordinates
    - occupy 'space'
    - real polygons: lake, field, stand of trees
    - "imaginary polygons": administrative units
  - (Surfaces)
    - "3 dimensions" ("has volume")
    - classically it is a topographic surface ... 2.5 dimensions
- ArcGIS
  - GCS
    - refers to datum
    - "version" of lat/long
    - NAD83, NAD 27
    - WGS84
      - common for world
      - used for GPS
      - very close to NAD83 for NA
  - PCS
    - cartesian ... maps are planar
    - GIS 'draws' to a cartesian system
    - but it first converts from the sphere
    - UTM - only PCS studied
  - Spatial Data
    - grouped into layers (themes)
      - map features ... coordinates
      - descriptive attributes ... database
      - one-to-one relationship of map feature - record in a table
    - point or line or polygon
- Data Sources
  - GeoBC - iPad Download of "1:20,000"
  - thematic maps
    - VRI (forest cover)
    - fresh water
    - others
  - satellite (Google Earth, SPOT, Landsat, Quickbird)
  - air photos (orthophoto)
  - Field Survey
    - notes -> RoadEng -> export
    - GPS (corrected and downloaded)