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GIS flow modelTypes of ErrorsPropagation Of ErrorsModeling Techniques
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!
1. GIS Flow Model Capture Data Register Map Base Interpret Store Data Datain Computer Convert Data to Digital Process Format Data Display Results
TIME LINEACTION FORECASTING PREDICTION PRESENT FUTURE
Black Box ModelINPUT OUTPUT S/M PSEUDO BLOCK MODEL
2. TYPES OF ERRORS• GROSS ERRORS• RANDOM ERRORS• SYSTEMATIC ERRORS
GROSS ERRORSCaused due to carelessness and human errorsPrevention by series of checks and implementing sound procedures thatminimize 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 dataMinimizationCareful measurementMeasurement system design
SYSTEMATIC ERRORS Models of the process we are using Caused by mismatch between Reality of the process Detection1. By Analysis of error propagation2. By sensitivity analysis3. By parameter evaluation
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 .
Data Structure…. GIS GRAPHIC ALPHA NUMERIC VECTOR RASTERCO-ORDINATE IMAGE SYSTEM AREAL REMOTE SENSED PHOTOGRAPH SCANNED 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. 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.
Comparison of Raster and Vector FormatsMost GIS software can display both raster andvector data. Only a limited number of programscan analyze both types of data or make raster typeanalyses in vector formats.
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
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 4. Modeling Techniques Mobile GIS PC, PDA Phone Desktop GIS Network Virtual Globes Server GIS Geo databases XML Files DBMS
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.
Grid sampling examples within hexagonal grid A number of GIS software packages, such as TNTMips, ENVI, Idrisi and GRASS providetools 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 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.
How to GeomaskOutside 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
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
U.S. Census Bureau TIGER GEOCODER TOPOLOGICALLY NTEGRATED EOGRAPHIC I NCODING G EFERENCING E GIS 45
Software Used Arc/Info IDRISI Also use: ER-Mapper, ERDAS, Atlas*GIS
Textbooks 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
• 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