This document discusses geographic information systems (GIS) including: 1. A GIS flow model showing the typical steps of capturing, storing, processing, and displaying geospatial data. 2. Types of errors in GIS like gross errors from human error, random errors inherent in measurement, and systematic errors from mismatches between models and reality. 3. How errors can propagate through a GIS as one error leads to others, corrupting the entire system. 4. Different modeling techniques used in GIS like vector and raster data structures, and mobile, desktop, server, and virtual globe applications.

1. ICGE 2012 - December 3-4,2012 (Paper No. D005)

2. GIS flow model
Types of Errors
Propagation Of Errors
Modeling Techniques

3. Geographic Information System
• Geographic – 80% of government data collected is
associated with some location in space
• Information - attributes, or the
characteristics (data), can be used to symbolize and
provide further insight into a given location
• System – a seamless operation linking the
information to the geography – which requires
hardware, networks, software, data, and operational
procedures
…not just software!
…not just for making maps!

4. 1. GIS Flow Model
Capture
Data
Register
Map Base
Interpret
Store Data Data
in Computer Convert Data
to Digital
Process Format
Data
Display
Results

5. Challenges of GIS

6. Accuracy and Precision

7. ERROR AND UNCERTAINTY

8. SOURCES OF ERROR

9. HANDLING ERROR

10. HANDLING ERROR

11. TIME LINE
ACTION FORECASTING
PREDICTION
PRESENT FUTURE

12. Black Box Model
INPUT OUTPUT
S/M
PSEUDO BLOCK MODEL

13. 2. TYPES OF ERRORS
• GROSS ERRORS
• RANDOM ERRORS
• SYSTEMATIC ERRORS

14. GROSS ERRORS
Caused due to carelessness and human errors
Prevention by series of checks and implementing sound procedures that
minimize the opportunities for these types of errors to occur

15. RANDOM ERRORS
Are intrinsic to the measurement process. & exhibit definite statistical behaviour.
Random errors can only be eliminated by carefully examining large amounts of
redundant data
Minimization
Careful measurement
Measurement system design

16. SYSTEMATIC ERRORS
Models of the process we are using
Caused by mismatch between
Reality of the process
Detection
1. By Analysis of error propagation
2. By sensitivity analysis
3. By parameter evaluation

17. Initial processing errors
1. Topology
2. Layer Matching
3. Edge Matching
4. Topological Construction
5. Feature Identification
6. Lineage

18. LAYER MATCHING

19. Lineage or processing history
• A collection of states representing the changes
that have occurred over time in a versioned geo
database.

20. Metadata
 Metadata is data about data.
It is a summary document providing :
1. content,
2. quality,
3. type,
4. creation,
5. and spatial information about a dataset.

21. Meta data Analysis

22. Digitizing and Geocoding Errors
 Processing errors occur
during other phases of data
manipulation such as :
1. Digitizing and geocoding.
2. Overlay and boundary
intersections.
3. Errors from rasterizing a
vector map.
 Physiological errors of the operator may result in :
1. Spikes.
2. Switchbacks.
Again you cannot be lazy!
3. polygonal knots.
4. loops .

23. Data Structure….
GIS
GRAPHIC ALPHA NUMERIC
VECTOR RASTER
CO-ORDINATE IMAGE
SYSTEM
AREAL REMOTE SENSED
PHOTOGRAPH SCANNED IMMAGES

24. Vector and Raster data
• The vector model is extremely useful for
describing discrete features, but less useful for
describing continuously varying features such as
soil type or accessibility costs for hospitals.
What is the resolution of the data?
If raster, report cell size
If vector, report scale
• The raster model has evolved to model such
continuous features. A raster image comprises a
collection of grid cells rather like a scanned map
or picture.

25. Comparison of Raster and Vector
Formats
Most GIS software can display both raster and
vector data. Only a limited number of programs
can analyze both types of data or make raster type
analyses in vector formats.

26. 3. PROPAGATION OF ERRORS:
Σ
• Propagation occurs when
one error leads to another ,
• Eg: If a map registration point has been mis-digitized in one
coverage and is then used to register a second coverage, the second
coverage will propagate the first mistake. In this way, a single error
may lead to others and spread until it corrupts data throughout the
entire GIS project.
How To avoid this problem ? ? ?
use the largest scale map to register your points

27. Why Use GIS in Schools?

28. Why Use GIS in Schools?
• Encourage seminars demonstrating applications
• Establish a networking organization encompassing all interested
disciplines
• Teach a class or lab for a department outside of your own
• Organize or team-teach a discipline-oriented workshop with a
domain expert
• Write proposals for non-GIS teaching, research and outreach
• Consider adopting a SpatialSTEM approach that translates grid-based map
analysis operations into a mathematical/statistical framework that serves as
the communal language of science, technology, engineering and
mathematics disciplines

29. GIS as infrastructure 4. Modeling Techniques
Mobile GIS
PC, PDA
Phone
Desktop GIS Network
Virtual Globes
Server GIS
Geo databases XML
Files DBMS

30. CONCLUSION –
 Gross errors are largely caused by carelessness and
human error.
 Systematic errors are caused by a mismatch between
the models of the processes
 Random errors are intrinsic to the measurement
process

31. REFERENCES :
1. BURROUGH, P.A., 1986. Principles of Geographical Information
Systems for Land Resources Assessment. Oxford, UK : Oxford University
Press.
2. CASSETTARI , S., 1993. Introduction to Integration Geo-Information
Management. London : Chapman and Hall.
3. CHRISMAN, N.R., 1983. The role of quality information in the long-term
functioning of a geographic information system. Cartographica 21 : 79.
4. CHRISMAN, N.R., and LESTER, M.K., 1991. A. Diagnostic Test for
Categorical Maps. Technical Papers 1991 ACSM – ASPRS Anual
Convention, Vol.6, pp. 330-348.
5. CHRISMAN, N.R., 1998. Rethinking Levels of Measurement for
Cartography. Cartography and Geographic Information System, Vol. 25,
No. 4, pp. 231 – 242.
6. DALE, P.F., and MCLAUCHLIN , J.D., 1999. Land Information
Management. Oxford University Press.
7. LAURINI, R., and THOMPSON, D., 1992. Fundamentals of Spatial
Information Systems. Sand Diego : Academic Press.
8. STAR, J.L and J.E. ESTES, 1990. Geographic Information Systems : An
Introduction, Prentice Hall.

36. Thank you.
QUERRIES ? ? ?

38. One More Thing
SYSTEM DYNAMICS

39. Grid sampling examples
within hexagonal grid
A number of GIS software packages, such
as TNTMips, ENVI, Idrisi and GRASS provide
tools to assist in the selection of sample points

40. Ontology-based model of space, time, and theme.
Spatial Occurrents and Named Places are directly linked
with Spatial Regions which record their geographic location.
Temporal intervals on relationships denote when the
relationship holds (valid time).
Courtsey : Analyzing Theme, Space, and Time: An Ontology-based Approach
By Matthew Perry – ACM 2006

41. Vector and Raster Formats
• Most GIS software can display both vector and
raster data.
• Raster formats are efficient when comparing
information among arrays with the same cell size.
• Raster files are generally very large because each
cell occupies a separate line of data.
• Vector formats are efficient when comparing
information whose geographical dimensions are
different.

43. How to Geomask
Outside a GIS
•Can perform arithmetic on X and Y (latitude
and longitude fields)
•Can set a minimum or maximum distance
based on population density (urban vs rural)
Inside a GIS
•Generate a random point within a circular
buffer
•Add a population density layer to decide
min/max distances
•Can avoid placing points “out of bounds”
GIS 43

44. Geocoding
Input
Address
yes Matches? no
Parse Address Score Matches
Generate Soundex Best Score no
for Address Name >= 90? Output
Rejects
yes
List Candidates: Correct Addresses
No. Range,Zone Output
Address or Map
GIS 44

45. U.S. Census Bureau TIGER
GEOCODER
TOPOLOGICALLY
NTEGRATED
EOGRAPHIC
I NCODING
G EFERENCING
E
GIS 45

46. Software Used
Arc/Info
IDRISI
Also use: ER-Mapper, ERDAS, Atlas*GIS

47. Textbooks
Geographic Information
Systems and Science, 3rd ed.
by Longley, Goodchild, Maguire,
and Rhind

48. Textbooks
GIS Tutorial 2: Spatial
Analysis Workbook for ArcGIS
10, 2nd ed.
by Allen

49. Textbooks
Place Matters: Geospatial
Tools for Marine Science,
Conservation, and
Management
in the Pacific Northwest
edited by Wright and Scholz

50. • To most folks on campus, geotechnology is simply a set of
highly useful apps on their smart phone or a 3D fly-by
anywhere in the world— in a sense trivializing GIS.

51. Source : Map Analysis , Joseph K. Berry, University of Denver; GeoTec Media publisher