Last updated April 10, 2022

Status: #📥/🟩 Tags: GEOG 150 Inputs #archivedCards/geog150

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' GEOG 150 Week 5

Class:: GEOG150

Notes

Exploring GIS: Georeferencing

Mapping the earth refers to two aspects ?

• Georeferencing
  • Scientific principles, process of transforming spatial data
• Symbolizing the map

Categories of spatial referencing systems

?

• Census geography (postal codes, DA, EA)
• Location specified by a label or code
• Location types are hierarchically aranged

Geocoding (postal address, COGO)

?

• Linear reference system
• Location specific by reference to a segment of a linear geographic feature and distance from that segment to a point
• Turning physical address into geographical point

Latitude, Longitude, UTM

?

• Coordinate reference system
• Location specified with respect to a datum
• Allows GPS point measurements

Georeferencing

What is georeferencing ?

• the principles and processes of transforming spatial data from an arbritrary system into a geographic or projected system

• Georeferencing process ?

1. Define correct shape of earth
2. Make it flat
3. Add coordinates
4. Group objects into communities

Models of earth

Globes ?

• Highly accurate
• Difficult to move around, time consuming to make, convenient for small scales

Ellipsoid ?

• Ellipsoid is more accurate than a sphere, takes flattening of earth into consideration
  • Each country used a different elipsoid 4:01

GEOID ?

• Accurate representation of earth’s shape and size
• Based on equipotential gravity surfaces at mean sea level
• Rock densitites cause the geoid to deviate from the elipsoid

• Datum is;; an accurate arrangement of ground points

• Horizontal datum;; provides a frame of reference for measuring locations on surface of earth

• Vertical datum;; provides a frame of reference for measuring elevations with respect to the mean sea level

• Removing datum results in 7 years in prison lmao

Geographic coordinate systems composition

?

• Key lines
  • Meridian, equator
• Related to 3d earth shape

Projected Coordinate Systems

• Mapping involves ?
• Determining geographic locations of features on earth’s curved surface, transforming locations into positions on a flat map
  • skinning the earth and laying it flat

• Earth projection can lead to distortion, but we can still preserve ?
• Angles (conformal/orthomorphic)
• Areas (equal-area or equivalent projections)
• Distances (equidistant projections)
• Directions (azimuthal and gnomonic projections)

• How to project earth ?
• Plane
  • Azimuthal projections
• Cylinder
  • Cylindrical projections
• Cone
  • Conic projections
• Each projection saves different properties

Universal Transverse Mercator (UTM) grid system

?

• world-wide system defined in meters
• Divided into
  • 60 zones, 6 degrees longitude each, 84 to 80
  • zone 1 is international date line

Spatial Data Representation

Real world to computer model

• Levels of conceptualization ?

1. Reality
2. Information model (Conceptual model)
   • (Objects/discrete features, fields/continuous features)
3. Representation of data model (Logical model)
4. Databases (Physical model)
5. File structures (Binary model)

Objects and fields

Objects ?

• Spatially referenced objects
• Boundaries defined
• Space is only occupied where objects exist
• Identified and described through attribute table

Field ?

• Vary across geographic space
• Fuzzy boundaries
• Exhaustive and exclusive
• Represented by category/value

Vector Data Model

?

• Points, vector lines, vector polygon
  • Names in spatial database
  • One geometry per layer

Specifying geometry for vector model (human world)

• Good for ?
• data with definite boundaries
• Network analysis capabilities
• Graphic output
• Used for census analysis, routing problems
• Branch of mathematics describing shape, size, and relative configurations of objects

• Topology focuses on properties of objects that don’t change when distorted ?
• Expresses spatial relationships between connected or adjacent vector features in a GIS database
  • Missing, system, user-defined
  • 
• Attribute table is linked to geometry

Raster data model (natural world)

• Good for ?
• Continuous data
• Good representation of spatial variability
• Good for data derived from remote sensing
• Forest change, landslide modeling
• Arranged in rows and column, each cell has a value

Choropleth map

?

• Used to show relative quantity by symbolizing area units such as countries, municipalities, using colour intensities

Thoughts/Questions

Backlinks

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Created:: 2021-10-07 16:10