1. Data source for Google earth
Satellite imagery
at least 15 meters of resolution
Aerial photography
the highest resolution, at 15 cm (6 inches)
Digital terrain model
NASA's Shuttle Radar Topography Mission
3D buildings for many major cities in the US and Japan
GIS
road, boundaries

2. Geographic coordinates (latitude/longitude) on the World Geodetic System of 1984 (WGS84) datum
Data: Usually less than 3 years old

3. How it works?
Google Earth approximate the sphere of the planet's surface with
flat tiles. The further away your viewpoint is
from the surface, the lower the resolution of these tiles can be.
Download high-resolution data
when the viewer is actively zooming towards it.
Images for places you have already looked at are stored
locally on your hard drive

4. Primary & Secondary Sources
Primary geographic data sources are captured specifically for use in GIS by direct measurement.
Secondary sources are those reused from earlier studies or obtained from other systems.

5. Classification of geographic data for data collection purposes
Raster
Vector
Primary
Satellite remote sensing
Aerial photographs
GPS measurements
Survey measurements
Secondary
Scanned maps or photographs
Digital elevation models from topographic map contours
Topographic maps

6. GIS Data: Primary & Secondary Sources
Primary data sources
Created “in house”
Through your own or your team’s field data collection
By transforming data from sources not yet available digitally
For use by the same organization
High level quality control
Often customized for specific project/application
Costly

7. Secondary Data Format conversion often required
Datasets may be difficult to find
Result: Data reproduced  costly redundancy
Data costs & sensitivity may limit access
Need to be aware of vendor’s quality control procedures to be able to judge data quality
What type of information included about data?
Scale, resolution, field names & descriptions, codes & meaning
Need enough info to be able to make decisions about whether data use is appropriate

8. Errors & Editing Types of errors: Entity error: Error in position
Attribute error: Incorrect attribution

9. Entity Errors
Undershoot
Overshoot
May be due to digitizing problems or fuzzy tolerance not set large enough
Prevention: Map preparation & setting appropriate tolerance level
Fix by snapping (undershoots), clipping (overshoots)
ArcGIS: Extend tool lets you click a line feature and extend it to another selected line feature; Trim tool lets you click a line feature and trim it to another selected line feature; The Snap fix will snap dangling line features to the nearest line feature within a given distance.
From Fundamentals of Geographic Information Systems, Demers (2005)

10. Entity errors Weird polygons: Polygons with missing nodes
Cause: Point digitized in wrong place or wrong order
Prevention: Map preparation or digitizing method
Fix: Moving lines to correct locations
Map prep – numbering points; Digitizing method – digitize in clockwise direction around polygon

11. Error in position:

12. Incorrect Attributes Missing attributes (e.g., -9999)
Incorrect attribute values
difficult to detect, both in raster and in vector

15. Sources for error: Hardware (digitizing, scanning) People Digitizing
Attribute inputs
Uncertainty in data transformation and analysis
Scanning –faint lines

16. Data & Editing
Before beginning a spatial analysis or mapping project  check data
Error detection and correction may include:
Compare data with input document
Check for missing spatial objects
Check attributes of spatial objects

17. Vector Editing Entities Attributes Entities & attributes together
Missing objects, incorrectly placed objects, incomplete links
Attributes
Typos, incorrect codes, attributes incorrectly associated with a field
Entities & attributes together
Codes associated with incorrect entities
Attribute & entity attribute errors most difficult to find
Tracking errors requires comparison to original data; examining input data & resultant map, resultant tables

18. After making changes: Incorrect attributes Rebuild topology Save!!
Changes modified some spatial relationships  topology needs to be updated
Save!!
Incorrect attributes
Prevention: Keep track of attributes as typing in
Fix: Correct them! Save!

19. Raster Data Editing Attribute values for grid cells Associated tables
Concerned with verification correct positions of grid cells
Examine column & row position, attribute code

20. Metadata Data about data
Content, quality, condition
Component of the GIS data input process  ArcCatalog
Why?
Organizations want to maintain their investment
To share information about available data
Data catalogs & clearinghouses
To aid data transfer & appropriate use
Maintain investment by cataloguing & noting appropriate use of data

21. Introduction to Maps Definition
A graphic depiction on a flat medium of all or part of a geographic realm in
which real world features have been replaced with symbols in their correct
spatial location at a reduced scale.
Map: to transform information from one form to another
--- Mathematics
The term “map” is often used in mathematics to convey the notion of transforming information from one form to another, just as cartographers transfer information from the surface of the Earth to a sheet of paper.
The term “map” is used loosely to refer to any visual display of information.
map
Earth surface
Paper
--- Geography

22. Types of Map Topographic Map: Thematic Map:
A map showing the outlines of selected natural and man-made features
of the Earth. It also shows roads and other prominent features.
Topography = shape of the surface
Thematic Map:
A map showing the spatial patterns of a geographic theme, such as land
use, climate, population etc.

23. Characteristics of Maps
• Abstracted – requires careful interpretation
• Show only static situation --- one slice in time
• Often highly artistic
Map making is as much an art as it is a science.
• Usually out of date
• Questions easy to answer by maps
○ how to get there from here?
○ what is at a certain location?
• Questions difficult to answer by maps
○ what is the area of this lake?
○ what can I see from here?
○ what this point on the topo map is on the thematic map

24. Maps and GIS Disadvantage of Paper Maps
Consistent, accurate retrieval of data from maps is difficult
Only limited amount of info can be show due to constraints of paper
Advantage of Digital Maps
Remote access
High density of info.
Powerful map analysis (impossible with paper maps)
Accurate and rapid measurement of area
Spatial analysis
GIS offers significant advantages of map display over paper map
Zoom to change scales freely
Allows 3-D perspective views

25. Map elements Most common: map/spatial data title legend scale
north arrow
inset(s)
textual information (incl. spatial metadata)
border, neatlines
coordinate grid

26. Map Elements Legend Scale Credits North Arrow Place name Inset Ground
Figure
Neat line
Border
Title
Figure: The area of interest (area being mapped)
Ground: background

27. Major Map Elements Necessary components of a typical map Title
Legend: Interpretive key to symbols
Symbols: Used to describe features
Scale bar
North arrow

28. The ratio between map distances and Earth Distances.
Scale Issues
Map Scale:
The ratio between map distances and Earth Distances.
Something from the Earth…
(a geographic entity or phenomenon)
… is scaled to be mapped at a much smaller size.
Note: We must always be aware of the implications of scale
when using geographic data

29. General Classification of Scale
Large scale
1:400 to 1:50,000
Intermediate scale
1:50,000 to 1:250,000
Small scale
1:250,000 and beyond
The scale used for most U.S. topographic mapping is 1:24,000

30. 1:100,000
1:24,000

31. Representing Scale on Maps
representative fraction “1:50,000”
Verbal “1 inch = 50 miles”
Graphic scale
10 miles
Questions: How many miles does 5 cm map distance represent in
the real world on a map of 1:320,000? How many kilometers does
5 inches represent in the real world on a map of 1:100,000?

32. What is the real world distance for 10 cm on a map with a scale of 1:500,000?
(A) 50 km.
(B) 500 km.
(C) 100 km.
(D) Not enough information to answer the question.