Spatial Data 1-Introduction to GIS 5/9/2018 © J.M. Piwowar

Why is Geographical Information Special? 1-Introduction to GIS 5/9/2018 Why is Geographical Information Special? Integration of spatial data from various sources can be time-consuming and tedious Updating geographic data is complex and expensive Cartographic displays of geographic data require the retrieval of large amounts of data Multidimensional requires 2 coordinates to define a location Voluminous GIS databases can easily reach a terabyte in size (1 Tb = 1000 Gb) Often requires projection onto a flat surface Requires specialized analysis methods Integration of spatial data from various sources can be time-consuming and tedious Updating geographic data is complex and expensive Cartographic displays of geographic data require the retrieval of large amounts of data © J.M. Piwowar Spatial Data © J.M. Piwowar

Why is Geographical Information Special? 1-Introduction to GIS 5/9/2018 Why is Geographical Information Special? Representations of the real-world Imprecise Multidimensional Voluminous Often requires projection onto a flat surface Requires specialized analysis methods Multidimensional requires 2 coordinates to define a location Voluminous GIS databases can easily reach a terabyte in size (1 Tb = 1000 Gb) Often requires projection onto a flat surface Requires specialized analysis methods Integration of spatial data from various sources can be time-consuming and tedious Updating geographic data is complex and expensive Cartographic displays of geographic data require the retrieval of large amounts of data © J.M. Piwowar Spatial Data © J.M. Piwowar

Why is Geographical Information Special? 1-Introduction to GIS 5/9/2018 Why is Geographical Information Special? Multidimensional requires 2 coordinates to define a location Voluminous GIS databases can easily reach a terabyte in size (1 Tb = 1000 Gb) Often requires projection onto a flat surface Requires specialized analysis methods Integration of spatial data from various sources can be time-consuming and tedious Updating geographic data is complex and expensive Cartographic displays of geographic data require the retrieval of large amounts of data © J.M. Piwowar Spatial Data © J.M. Piwowar

How do we Represent Geography? 1-Introduction to GIS 5/9/2018 How do we Represent Geography? Space, Time, Attribute © J.M. Piwowar Spatial Data © J.M. Piwowar

1-Introduction to GIS 5/9/2018 What is a Map? a representation, normally to scale and on a flat medium, of a selection of material or abstract features on, or in relation to, the surface of the earth a model of spatial phenomena; an abstraction; not a miniature version of reality a map is a cartographic abstraction maps are the most common way of recording geographic information maps are the main data source and principal product of a GIS What is a Map? a representation, normally to scale and on a flat medium, of a selection of material or abstract features on, or in relation to, the surface of the earth a model of spatial phenomena; an abstraction; not a miniature version of reality a map is a cartographic abstraction Cartographic Abstraction selection simplification exaggeration Symbolization Questions Maps Can Answer easy questions how do I get from there to here? what is at this point? more difficult or time-consuming questions what is the area of this lake? what places can I see from this scenic lookout what does that thematic map show at the point I am interested in on this topographic map? © J.M. Piwowar Spatial Data © J.M. Piwowar

Types of Maps topographic © J.M. Piwowar Spatial Data

Types of Maps thematic 1-Introduction to GIS 5/9/2018 a choropleth map uses reporting zones such as counties or census tracts to show data such as; average household income, education level, or crime rates. the boundaries of the zones are established independently of the data, and may be used to report many different sets of data © J.M. Piwowar Spatial Data © J.M. Piwowar

Important Properties of Maps Scale Coordinate System Projection © J.M. Piwowar Spatial Data

Scale The ratio between distances on the map and corresponding distances in the real world Representations: Statement: 1 cm = 100 km Representative Fraction (RF): 1:50,000 Graphic: © J.M. Piwowar Spatial Data

Coordinate Systems Where is the University of Regina? City of Regina 3737 Wascana Pkwy S4S 0A2 Map grid: K-11 50° 15’ 05” N 104° 21’ 09” W 528904E 5585457N NAD83 © J.M. Piwowar Spatial Data

1-Introduction to GIS 5/9/2018 Latitude & Longitude Latitude and longitude: the framework of the international reference system that pinpoints a place's absolute location. Latitude: describes how far north or south of the equator a place is, measured in degrees. each degree (written: 58°) is divided into 60 minutes (written: 42') and each minute into 60 seconds (written: 26"). e.g. 58° 42' 26" N 1° latitude is approximately 110 km (69 mi.). © J.M. Piwowar Spatial Data © J.M. Piwowar

1-Introduction to GIS 5/9/2018 Latitude & Longitude Longitude: position east or west of a half circle drawn from the North to the South Pole and passing through the former Royal Observatory at Greenwich, London, England . Such lines joining places of the same longitude are called meridians of longitude. e.g. 105° 02' 56" W © J.M. Piwowar Spatial Data © J.M. Piwowar

Ellipsoids Polar coordinates are useful for describing locations on the globe. But! The Earth is not a sphere. Clarke, K.C., 2003. Getting Started with Geographic Information Systems.. Prentice-Hall © J.M. Piwowar Spatial Data

What about Elevations? How high is something? Sea level Gravity models 1-Introduction to GIS 5/9/2018 What about Elevations? How high is something? Sea level Gravity models The topographical surface of the earth is the actual surface of the land and sea at some moment in time. Aircraft navigators have a special interest in maintaining a positive height vector above this surface. Sea level is the average (methods and temporal spans vary) surface of the oceans. Tidal forces and gravity differences from location to location cause even this smoothed surface to vary over the globe by hundreds of meters. Gravity models attempt to describe in detail the variations in the gravity field. The importance of this effort is related to the idea of leveling. Plane and geodetic surveying uses the idea of a plane perpendicular to the gravity surface of the earth, the direction perpendicular to a plumb bob pointing toward the center of mass of the earth. Local variations in gravity, caused by variations in the earth's core and surface materials, cause this gravity surface to be irregular. © J.M. Piwowar Spatial Data © J.M. Piwowar

Geoid Models Geoid models attempt to represent the surface of the entire earth over both land and ocean as though the surface resulted from gravity alone. Peter H. Dana, The Geographer's Craft Project, Department of Geography, The University of Colorado at Boulder © J.M. Piwowar Spatial Data

1-Introduction to GIS 5/9/2018 Datums A mathematical formula that combines an ellipsoid and its geoid fit to surveyed control points. NAD27 NAD83 WGS84 1900 US Standard Datum first nationwide datum Clark 1866 spheroid origin Meades Ranch, Osborne Cnty KS determined by visual triangulation approx. 2,500 points renamed North American Datum (NAD) in 1913 when adopted by Mexico and Canada NAD27 Meades Ranch origin visual triangulation 25,000 stations (250,000 by 1970) NAVD29 (North American Vertical Datum, 1929) provided elevation basis for most USGS 7.5 minute quads NAD83 satellite (since 1957) and laser distance data showed inaccuracy of NAD27 1971 National Academy of Sciences report recommended new datum used GRS80 spheroid (functionally equivalent to WGS84) origin: Mass-center of Earth 275,000 stations NAVD88 provides vertical datum points can differ up to 160m from NAD27, but seldom more than 30m, and data from digit. map more inaccurate than datum diff. completed in 1986--but gps more accurate! WGS84 World Geodetic System same as NAD83 basis for GPS © J.M. Piwowar Spatial Data © J.M. Piwowar