L5.3: Spatial Concepts: Geo-referencing & Map Projections PDF

# UTM - The Universal (UTM) projection zones of degree latitude. - 1 central line per zone - 2 Standard lines per zone (180 km to the west & the east of central line) ## Transverse (cylinder axis perpendicular to the globe axis) ## Mercator Projection (conformal) ## On the Fly Projection By defaul...

# UTM - The Universal (UTM) projection zones of degree latitude. - 1 central line per zone - 2 Standard lines per zone (180 km to the west & the east of central line) ## Transverse (cylinder axis perpendicular to the globe axis) ## Mercator Projection (conformal) ## On the Fly Projection By default, a map in a scene is assigned the coordinate system of the first feature layer you add to it. Subsequent feature layers with different coordinate systems are projected to the map’s spatial reference (on-the-fly) in real time. # Projection ## Process of transforming the spatial relationship of phenomena on Earth’s surface (3D) into a plane (2D); transform from 3D to 2D. ## Surface Measures - Geographic Coordinates - Angle: Lat/West - Angle - Cartesian coordinates ## Projecting 3D to 2D induces potential distortions: - Distance - Area - Shape # Map Projections - **Conformal**: Preserves local angles & shapes. - **Equivalent**: Represents areas correctly (relative size). - **Equidistant**: Maintains constant scale along certain areas. - **Preserved properties are important for thematic mapping.** ## Tissot indicator - Shows local distortion of parts of a map caused by the used map projection. - **What type of distortion occurs in the size, shape & orientation. Commonly placed at the intersections of parallels & meridians** # Lecture 5: Spatial Concepts: Geo-referencing & Map Projections ## Why do we need projections? - Earth is in 3D. - Maps will be in 2D - We need a compromise. ## Spatial features on the earth surface (3D) are represented by geographic coordinate systems expressed in: - **Latitude, Longitude.** - **Measurement in angular units.** - **Latitude:** based on parallels (north, south) - **Longitude:** based on meridians (east, west). - **Angle:** between the prime meridian & the location. - **Angle:** between the equatorial plane & the location. - **Horizontal Datum**: (ellipsoid) for location - **Mathematical Model** - **Origin** - **Vertical Datum**: (geoid) for Elevation - **Physical Model** # There are numerous models of the earth: - **Equator**: The reference frame of the coordinate system. - **Prime Meridian**: The reference meridian (longitude) usually 0°. - **Geodetic Datum**: The basis for geographical coordinates of a location which defines the size & shape of the earth and the origin & orientation of the coordinate systems used to map the earth, serves as reference for calculating the geographical coordinates. - **So ellipsoid = Shape** - **Datum: Anchors the ellipsoid to a specific location.**