1. CE 250 - Introduction to Surveying and Geographic Information Systems
eLearning Version
Donald J. Leone, Ph.D., P.E.
Lecture 2

2. Introduction Spatial Data – How is it described?
Spatial Data – Main sources.
More on Rasters and Vectors
Spatial Data Models
Two new Spatial Data Entities
Numerical Characteristics of Attributes.

3. Definition
Spatial Data: Information about the geographic position of features
Geographic Position – Usually an x,y coordinate pair in two dimensional space

4. GIS Model Building Model – “Simplified “ view of the “real” world.
Computer generated representation.
Constructed using spatial data.

5. Nature of Spatial Data Data vs. Information - Metadata
Primary data – first hand knowledge
Secondary data – collected by someone else
Spatial data types
Temporal – when, where, etc. (Metadata)
Thematic – describes real world feature (Attributes)
Spatial – location of feature (x,y)

6. Traditional Maps Influence how we characterize spatial data. Purpose
Scale
Select features
Adopt a map projection
Select a spatial reverencing system
Annotate

7. Scale Definition – Indicates how much smaller than reality a map is.
Ratio – Distance on a map to the distance on the ground.
1:5000 – 1 cm on map = 5000 cm on ground or 50 m
Graphical
1 cm 0m
50m
100m
150m

8. Scale – Continued “small scale maps” Cover large areas
Large ratio’s – 1:2,000,000
“small scale maps”
Cover large areas
Small ratio’s – 1:25,000
“large scale maps”
Cover small areas

9. Scale Related Generalization
The level of detail shown is directly related to scale

10. Map Projections Transfer spherical earth to flat surface.
Many types of projections used world-wide.
There will always be some distortion generated in the projection process.

11. Projection Techniques Cylindrical Projection

12. Projection Techniques Azimuthal Projection

13. Projection Techniques Conic Projection

15. Spatial Referencing Geographic Coordinate Systems (3D)
Rectangular Coordinate Systems (2D)
Non Coordinate Systems, i.e. zip codes

16. Geographic Coordinate System Latitude and Longitude
Parallels
- Meridians

17. Geographic Coordinate System Latitude and Longitude Angles
Prime Meridian
00 Longitude
Latitude – North
Longitude - West
Equator
00 Latitude

18. Latitude – Longitude Calculation

19. Little Grey Cells Quiz Large scale maps cover large areas. T or F
Why are projections needed?
Why do you think the prime meridian goes through Greenwich, England?

20. Rectangular Coordinates (2D)

21. Universal Transverse Mercator (UTM)

22. The State Plane Coordinate System - SPCS
Used primarily for engineering applications
Arbitrary origin - An arbitrary number of feet south and west of the most southwesterly point on the map.
Eastings (x) and northings (y) all come out positive.
Advantage: Accuracy
Disadvantage: Lack of universality, as each state has it’s own coordinate system.

23. Break!

24. Other Sources of Spatial Data
Census Data – TIGER Files
Topolocally
Integrated
Geographic
Encoding
Referencing

25. Other Sources of Spatial Data
Aerial Photographs
Increased Altitude Produces smaller scale maps
Distortion toward the edges

26. University of Hartford Aerial Photo
Sports Center
HJG Center
UT Hall

27. Other Sources of Spatial Data
Satellite Images
LANDSAT Image Morro Bay, CA

28. Other Sources of Spatial Data
Surveying
The Global Position System – GPS

29. GIS Software Spatial Data Modeling Real World Spatial data – Map, etc.
Raster
Vector
GIS
Software
Spatial
Data
Structure
Computer

30. Raster Data Structure
Feature Model
Cell Values
File Structure

31. Vector Data Structure
Line or Arc Number
Node or Point Number

32. Vector Data Structure - TOPOLGY
Topology - “The property that describes adjacency and connectivity of features”
Newer structure for Vector data - Topological Arcs File - added to previous data.
Used to build polygons that touch each other exactly.

33. Vector Data Structure - TOPOLGY

34. Two New Spatial Entities
“Old” three – Points, Lines, Polygons
Add two more –
Surfaces
Networks

35. Surfaces
Snowdonia National Park, Wales

36. Surfaces
Snowdonia National Park, Wales

37. Raster Digital Terrain Models – DTM
Digital Elevation Model (DEM) - Njolomole, Malawi

38. Vector DTM’s Triangular Irregular Network - TIN

39. TINS - Surface Significant Points
Eliminate points that are close together and similar – Cuts down on storage requirements.
Those points that cannot be interpolated from their neighbors – Surface Significant.
Surface Significant points are used as vertices in the TIN

41. Modeling Networks
Network – “A set of interconnected line features through which material, goods and people are transported. or
Along which communication of information is achieved.”

42. Networks
Impedance – The cost associated with traversing a network link, making a turn, or stopping.

43. Raster and Vector Data Models

44. Raster and Vector Data Models

45. Thematic Characteristics of Spatial Data aka - Attributes
Gives information about the feature.
Allow certain GIS operations – like “Query”.
Scale of measurement of the attributes is important.

46. Scales of Measurement of the Attributes
Nominal: Assign a label or class to a feature, e.g. 1 is a well, 2 is a catch basin.
Ordinal: Have a rank assigned to them e.g. 1 is light, 2 moderate, 3 heavy.
Interval: Values measured on relative scale e.g. elevations measured from some datum.
Ratio: Values measured on an absolute scale e.g. coordinates or total precipitation.

47. How to Construct a Spatial Data Model
Purpose
Scale
Select features
Adopt a map projection
Select a spatial reverencing system
Annotate

48. What’s Next
Attribute Data Management.
Data Input and Editing.