GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl A model is a ‘synthesis of data’ + information about how the data interact. Geographical data are locations and attributes at locations... What is a model?

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl locational data (x,y) + attribute data (z) = a spatial data model What results from the locational referencing of geographic attribute data? From the infinite numbers of objects, their characteristics and relationships in the world, a limited set is selected. The result is a conceptual model of reality.

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl The conceptual model of reality becomes, in a GIS, a logical data model encoded in digital form. This allows us to visualize it and work with it using computer technology. +=

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Locational Systems 1. Geographical co-ordinates (  ) Methods of describing locations on the earth’s surface or on maps of the earth’s surface 2. UTM co-ordinates (E, N)

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Latitude, , of a point: the angular distance north or south of the equator Longitude,, of a point: the angular distance east or west of a designated meridian Meridian: a line of constant longitude Parallel: a line of constant latitude

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Equator  = 0º = 0º Prime Meridian = 0º = 0º Co-ordinates of point P = 

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Ellipsoid: a description of the shape of the earth Peter H. Dana, The Geographer's Craft Project, Department of Geography, The University of Colorado at Boulder. See:

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Datum: a reference system for surveying and mapping vertical datum: a level surface to which elevations are referenced horizontal datum: a network of control points based on a description of the earth’s shape, used as a reference for position

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl North American horizontal datums : 1. NAD 27 - based on the Clarke 1866 ellipsoid 2. NAD 83 - based on the GRS80 (WGS84) ellipsoid

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl The UTM is both a map projection and a rectangular grid system for spatial referencing The Universal Transverse Mercator co-ordinate system

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl a UTM zone is 6º wide How many zones are there in total?

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Ottawa is near the central meridian of zone 18. There are 60 zones, numbered 1-60 from 180º West to East

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Superimposed on the zone is a rectangular grid. The basic grid lines are 100,000 metres (100 km) apart. The grid lines coincide with the equator and the central meridian of the zone.

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl False origin (0,0) 500,000 m The False Origin for the northern hemisphere for UTM co-ordinates (eastings and northings) is 500,000 metres west of the intersection of the equator and the central meridian of the zone.

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl MTM (Modified Transverse Mercator) co-ordinates: Instead of 60 x 6º zones, the MTM system has 120 x 3º zones. The False Origin is 304,800 metres from the central meridian of the zone. MTM co-ordinates are used in Canada in Quebec and Nova Scotia.

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl All GIS’s store maps and map data as numbers. There are two main models for structuring these data: raster vector Spatial data structures

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Raster data: use a grid or cell structure to hold the data. Vector data: composed of points represented by exact co- ordinates which define points, lines, & polygons.

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl point - pair of co-ordinates line - series of points start node end node polyline - multiple arcs start node end node vertex

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl polygon - series of lines enclosing an area start/end node vertex

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Kenneth E. Foote and Donald J. Huebner, The Geographer's Craft Project, Department of Geography, The University of Colorado

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Kenneth E. Foote and Donald J. Huebner, The Geographer's Craft Project, Department of Geography, The University of Colorado

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Advantages: Simple data structure Compatible with remotely sensed or scanned data Simple spatial analysis procedures Disadvantages: Requires greater storage space on computer Depending on pixel size, graphical output may be less pleasing Projection transformations are more difficult More difficult to represent topological relationships Kenneth E. Foote and Donald J. Huebner, The Geographer's Craft Project, Department of Geography, The University of Colorado Raster structure

GEOG 2007A An Introduction to Geographic Information SystemsFall, 2004 C. Earl Advantages: Requires less disk storage space Topological relationships are readily maintained Graphical output more closely resembles hand-drawn maps Disadvantages: More complex data structure Not as compatible with remotely sensed data Software and hardware are often more expensive Some spatial analysis procedures may be more difficult Overlaying multiple vector maps is often time consuming Kenneth E. Foote and Donald J. Huebner, The Geographer's Craft Project, Department of Geography, The University of Colorado Vector structure