GIS Lecture 3 Notes PDF

1. Introduction to Georeferencing ​ Definition: Georeferencing refers to the process of associating data with a specific location on Earth using coordinate systems. ​ Purpose: Enables GIS to represent features accurately on a map. Key Properties of Georeferencing Systems 1.​ Unique...

1. Introduction to Georeferencing ​ Definition: Georeferencing refers to the process of associating data with a specific location on Earth using coordinate systems. ​ Purpose: Enables GIS to represent features accurately on a map. Key Properties of Georeferencing Systems 1.​ Uniqueness: Locations must be uniquely identifiable (e.g., distinguishing Springfield, MO, from Springfield, UK). 2.​ Persistence: Locations remain consistent over time. 3.​ Spatial Resolution: Specifies level of detail (e.g., "Norman" is more precise than "Oklahoma"). 4.​ Metric vs. Non-Metric: ○​ Metric: Uses coordinate systems to calculate distances mathematically (e.g., lat/long). ○​ Non-Metric: Uses relative locations (e.g., "next to the river"). 2. Geographic Coordinate System (GCS) ​ Description: Uses latitude and longitude lines to specify locations. ​ Components: ○​ Latitude (Parallels): Measures north-south position. ​ Ranges from 0° at the equator to ±90° at the poles. ○​ Longitude (Meridians): Measures east-west position. ​ Ranges from 0° at the Prime Meridian (Greenwich, England) to ±180°. ​ Units: Angular degrees, minutes, and seconds (or decimal degrees). ○​ Example: Norman, OK = 35°13'N, 97°26'W. Terms to Remember ​ Meridian: A line of constant longitude. ​ Parallel: A line of constant latitude. ​ Unprojected Nature of GCS: Cannot compute accurate areas or distances without projection. 3. Map Projections ​ Purpose: Converts Earth’s 3D surface into a 2D map. ​ Challenges: Introduces distortions in:  ○​ Area: Size of features. ○​ Shape: Geometric appearance. ○​ Distance: Space between points. ○​ Direction: Angles or bearings. Projection Properties 1.​ Equal-Area (Equivalent): Preserves area but distorts shape. 2.​ Conformal (Orthomorphic): Preserves shape but distorts area. 3.​ Equidistant: Preserves distances (only in specific areas). 4.​ True-Direction (Azimuthal): Preserves angles/directions. 5.​ Compromise: Balances distortion among properties. Projection Factors 1.​ Developable Surfaces: Shapes onto which the Earth is projected. ○​ Cylindrical: Gridlines form rectangles (e.g., Mercator). ○​ Conical: Gridlines curve (e.g., Albers Equal Area). ○​ Planar: Gridlines radiate from a central point (e.g., Azimuthal). 2.​ Aspect: Orientation of the developable surface. ○​ Normal: Aligned with the poles. ○​ Transverse: Aligned with the equator. ○​ Oblique: At an angle. 3.​ Viewpoint: Light source for projection. ○​ Gnomonic: From the Earth's center. ○​ Stereographic: From the far side of the globe. ○​ Orthographic: From infinity. 4.​ Case: Intersection of the developable surface with Earth. ○​ Tangent: Touches at one line or point. ○​ Secant: Cuts through the Earth. 4. Common Map Projections 1.​ Albers Equal Area: ○​ Type: Conic. ○​ Properties: Preserves area; distorts shape, distance, and direction. ○​ Uses: Regional/national maps. 2.​ Lambert Conformal Conic: ○​ Type: Conic. ○​ Properties: Preserves shape and direction; distorts area. ○​ Uses: Navigation, State Plane Coordinate System. 3.​ Mercator: ○​ Type: Cylindrical.  ○​ Properties: Preserves direction and shape; distorts area at high latitudes. ○​ Uses: Navigation, world maps. 4.​ Azimuthal Equidistant: ○​ Type: Planar. ○​ Properties: Preserves distances and directions from a central point. ○​ Uses: Polar maps, air/sea navigation. 5. Projected Coordinate Systems (PCS) ​ Definition: A grid superimposed on a map projection to specify locations in a plane. ​ Components: ○​ Ellipsoid: A mathematical model of Earth’s shape (e.g., GRS80, WGS84). ○​ Datum: Links the ellipsoid to specific Earth locations (e.g., NAD83). ○​ Projection: Converts the 3D Earth into 2D coordinates. Common PCSs 1.​ Universal Transverse Mercator (UTM): ○​ Divides the globe into 60 zones, each 6° wide. ○​ Uses meters for coordinates (e.g., easting and northing). ○​ Popular for GPS mapping. 2.​ State Plane Coordinate System (SPCS): ○​ Divides states into smaller zones to minimize distortion. ○​ Uses different projections (e.g., Lambert for wide zones, Mercator for tall zones). 6. Practical Applications ​ GCS vs. PCS: ○​ GCS: Based on lat/long; unprojected; suitable for global contexts. ○​ PCS: Projected; allows accurate distance, area, and direction measurements. ​ Choosing the Right Projection: ○​ Depends on the purpose of the map: ​ Preserve area for population density studies. ​ Preserve distance for transportation routes. ​ Preserve direction for navigation.