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

2. 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

3. 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

4. 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

5. 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

6. 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

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

8. 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

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

10. 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

11. 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 N NAD83
© J.M. Piwowar
Spatial Data

12. 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

13. 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

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

15. 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

16. 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

17. 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 but gps more accurate!
WGS84 World Geodetic System
same as NAD83
basis for GPS
© J.M. Piwowar
Spatial Data
© J.M. Piwowar