COORDINATE SYSTEMS IN GIS As GIS is based

COORDINATE SYSTEMS IN GIS As GIS is based on geographic location you need to understand basics of Coordinate Systems: Geographic and Projected Coordinate Systems.

Geographic Coordinate Systems A geographic coordinate system (GCS) uses a three-dimensional spherical surface to define locations on the earth. A point is referenced by its longitude and latitude values In Arc. GIS: Longitude is X. Latitude is Y. http: //www. geographyalltheway. com Copyright © 2014 Natural Environmental Research Council (NERC) 2

Geographic Coordinate Systems Examples: WGS 84, OSGB 36, ED 50 • • • WGS 84 – basis for Global Positioning System (GPS). Geocentric, GRS 80 ellipsoid (ETRF 89, ITRF) OSGB 36 – basis for Ordnance Survey maps. Airy 1830 ellipsoid. European Datum 1950 – North Sea and mainland western Europe. International 1924 ellipsoid. Copyright © 2014 Natural Environmental Research Council (NERC) 3

Projected Coordinate Systems • Projections map the spherical Earth onto a plane. • Projections always: • Introduce discontinuities • Introduce distortions. http: //visual. merriam-webster. com/earth/geography/cartography/map-projections. php Try peeling an orange without breaking the skin!!! Copyright © 2014 Natural Environmental Research Council (NERC) 4

Projected Coordinate Systems • • Conformal – maintains shape Equal-area – maintains area Equidistant – maintains distance Direction – maintains some directions Copyright © 2014 Natural Environmental Research Council (NERC) 5

Datum • Defines the shape and orientation of an ellipsoid (mathematical representation of the earth) • Identifies the reference frame in use. – May be global • WGS 84 • ITRF series – May be local. • “Astronomical fix at Hope Bay” Copyright © 2014 Natural Environmental Research Council (NERC) 6

Projections recommended for mapping Antarctica • 1: 1 000 and smaller scales Antarctic Polar Stereographic / WGS 84 • 1: 1 000 to 1: 100 000 scales Lambert Conformal Conic or Polar Stereographic / WGS 84 • Scales larger than 1: 100 000 UTM / WGS 84 Note: to accurately analyse your data you need to use different projection!!! Copyright © 2014 Natural Environmental Research Council (NERC) 7

Map Scale Map scale is the relationship between the distance on a map and the distance on the Earth Small scale map Large scale map Copyright © 2014 Natural Environmental Research Council (NERC) 8