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

GIS flow model

Types of Errors

Propagation Of Errors

Modeling Techniques

Geographic Information SystemGeographic Information System

• Geographic – 80% of government data collected is associated with some location in space

• Information - attributes, or thecharacteristics (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!

CaptureData

1. GIS Flow Model1. GIS Flow Model

RegisterMap Base

InterpretData

Convert Datato DigitalFormat

Store Datain Computer

ProcessData

DisplayResults

Challenges of GISChallenges of GIS

Accuracy and Precision

ERROR AND UNCERTAINTY

SOURCES OF ERROR

HANDLING ERROR

HANDLING ERROR

TIME LINE

ACTION

PREDICTION

FORECASTING

PRESENT FUTURE

Black Box Model

S/MINPUT OUTPUT

PSEUDO BLOCK MODEL

2. TYPES OF ERRORS

• GROSS ERRORS

• RANDOM ERRORS

• SYSTEMATIC ERRORS

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

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 measurementMeasurement system design

SYSTEMATIC ERRORS Caused by mismatch between

Models of the process we are using

Reality of the process

Detection

1. By Analysis of error propagation2. By sensitivity analysis3. By parameter evaluation

Initial processing errors

1. Topology

2. Layer Matching

3. Edge Matching

4. Topological Construction

5. Feature Identification

6. Lineage

LAYER MATCHING

Lineage or processing history

• A collection of states representing the changes that have occurred over time in a versioned geo database.

MetadataMetadata

Metadata is data about data.Metadata is data about data.

It is a summary document providing : It is a summary document providing : 1.1. content, content, 2.2. quality,quality,3.3. type,type,4.4. creation, creation, 5.5. and spatial information about a and spatial information about a

dataset.dataset.

Meta data Analysis

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.3. polygonal knots.4. loops .

Again you cannot be lazy!

Data Structure….Data Structure….GIS

GRAPHIC ALPHA NUMERIC

VECTOR RASTER

CO-ORDINATESYSTEM

IMAGE

AREAL PHOTOGRAPH

REMOTE SENSEDSCANNED IMMAGES

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.

• 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.

What is the resolution of the data?

If raster, report cell size If vector, report scale

Comparison of Raster and Vector Comparison of Raster and Vector FormatsFormats

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.

3. PROPAGATION OF ERRORS:

• 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

Σ

Why Use GIS in Schools?

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

GIS as infrastructure

Virtual Globes

Desktop GIS

Server GIS

Mobile GISPC, PDAPhone

Network

DBMSFiles XMLGeo databases

4. Modeling Techniques

CONCLUSION – 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

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.

Thank you.

QUERRIES ? ? ?

One More ThingSYSTEM DYNAMICS

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

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 ApproachBy Matthew Perry – ACM 2006

Vector and Raster FormatsVector 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.

GIS 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 44

Geocoding

Matches?

Score Matches

InputAddress

Parse Address

Generate Soundexfor Address Name

List Candidates:No. Range,Zone

yes no

Best Score >= 90?

OutputAddress

OutputRejects

yes

no

Correct Addressesor Map

GIS 45

T IGER

OPOLOGICALLY

NTEGRATED

EOGRAPHIC

NCODING

EFERENCING

U.S. Census Bureau TIGER

GEOCODER

Software Used

Arc/Info IDRISI Also use: ER-Mapper, ERDAS, Atlas*GIS

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

and Rhind

Textbooks

GIS Tutorial 2: Spatial Analysis Workbook for ArcGIS 10, 2nd

ed.by Allen

Textbooks

Place Matters: Geospatial Tools for Marine Science, Conservation,

and Management in the Pacific Northwest

edited by Wright and Scholz

Textbooks

• 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. 

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