Spatial AnalysisAn Introduction to Concepts and theirImplementation in ArcMap

Description and AnalysisMost GIS systems are acquired by large organizations for the purpose of representing and describing features of the real world which are relevant to that organizations missionSpatial databases perform this functionMost concepts discussed so far relate to thisPoints, lines, polygons concepts for representationCoordinate systems as fundamental properties of spatial datageographic file formats for storageMost GIS system capabilities are focused hereAnalysis involves gaining an understanding of the patterns, and associated cause and effect processes, underlying the features which have been described in order toHelp the organization better carry out its missionMake better decisions, for exampleUnderstand the phenomena as a goal in itselfThis is the role of scienceGIS systems are less capable here, and often must be supplemented

Process, Pattern and AnalysisProcesses operating in space produce patternsSpatial Analysis is aimed at:Identifying and describing the patternIdentifying and understanding the process

Spatial Analysis: successive levels of sophisticationSpatial data manipulation: classic GIS capabilitiesSpatial queries & measurement, buffering, map layer overlaySpatial data analysis: descriptive and exploratoryVisualization through data manipulation and mappingJohn Snows maps of cholera in 1850s London

Spatial statistical analysis: hypothesis testingAre data to be expected or are they unexpected relative to some statistical model, usually of a random processSpatial modeling: predictionConstructing models (of processes) to predict spatial outcomes (patterns)What if analyses

GeoStatistics & Spatial StatisticsObject ViewThe real world is a series of entities located in space.An object is a digital representation of an entityObjects analyzed with Spatial StatisticsThe focus of this courseField ViewThe real world has properties which vary continuously over spaceevery place has a valueFields analyzed with GeoStatisticsThe focus of the Spatial Analysis course

The Pitfalls of Spatial AnalysisSpatial autocorrelationData from location near to each other are more likely to be similar than data from location remote from each otherCauses serious problems with traditional statistical modelsSpatial statistical models are essentialModifiable areal unit problem (MAUP)Results may depend on the areal unit usedCensus tracts versus counties (scale issue)Census tracts versus zip codes (not a scale issue)Ecological fallacyResults obtained from aggregated data (e.g. census tracts) cannot be assumed to apply to individual peopleA special case of the MAUP problemEncountered in spatial and non-spatial analysisScale affects representation and resultsCities may be points or polygonsMAUP may be viewed as a scale issueNonuniformity of Space and Edge IssuesPhenomena is not distributed evenly in spaceBank robberies cluster cos banks are clustered in spaceEdges, beyond which there is no data, can significantly effect results

Fundamental Spatial ConceptsDistanceThe magnitude of spatial separationEuclidean (straight line) distance often only an approximationAdjacencyNominal or binary equivalent of distanceLevels of adjacency exist: 1st, 2nd, 3rd nearest neighbor, etc..InteractionThe strength of the relationship between entitiesAn inverse function of distanceNeighborhoodAn association between one entity and those around itMay be based uponInteraction: flows or connections (functional)Similarity of attributes (formal)

Implementing Spatial Analysis in ArcGIS 9Primarily carried out in ArcMap:via Selection/Select by Locationthis selects features of one layer(s) which relate in some specified spatial manner to the features in another layer if desired, selected features may be saved later to a new theme via Data/Export DataIndividual features are not themselves modifiedvia Spatial Join (right click layer in T of C, select Join/Joins and Relates, then click down arrow in first line of Join Data window---see Joining Data in Help for details)Use for: points in polygon (identifies polygon in which point is located)lines in polygon (identifies polygons crossed by line)points on lines (to calculate distance to nearest line)points on points (to calculate distance to nearest neighbor point)operate on tables and normally creates a new table with additional variables, but again does not modify spatial features themselvesvia ArcToolbox Generally these tools modify geographic feature, thus they create a new layer (e.g. shape file)Tools are organized into multiple categories

DifferencesSelection: simply selects (highlights) entire spatial features in the target layer, but doesnt modify these featuresSelection onlyOnly Selected features (a subset of all features) are outputNo new output file saved unless you use Export/datajoins: operate on tables and normally creates a new table with additional fields or variables (columns), but again does not modify actual spatial features (rows) adds attributes (columns) to the layers table from another layers tableAll features are outputNo features modifiedNo new output file saved unless you use Export/dataAnalysis Toolbox (and others) in ArcToolbox Often these modify or create spatial features thus they output new spatial files

Different approaches can be used, in some cases, to produce same results.

Analysis Tools in ArcToolboxArcToolbox, particularly the Analysis Tools toolbox contains

Extract toolset, includingClip which limits one layer to the exact outer boundary of another layer(e.g. limit a Texas road theme to Dallas county only)Overlay toolset, includingIntersect, which combines two polygon layers--with output limited to common areaUnion, which combines two polygon layers--with output covering full extent of both layersProximty toolset, includingBuffer, for creating buffer polygons at a specified distance around points, lines or polygonsPoint Distance, for calculating distances between points within a specified radiusStatistics toolset, includingFrequency, which gives you counts of attribute value combinationsSummary Statistics, which gives you summary descriptive statistics for columns in a table, including sum, mean, min, max, etc..

Tools useful for analysis of vector data are located in other toolsets as well!!! For example: Data Management Tools>Generalization, containsDissolve, which removes boundaries between polgyons

The Components of An Analysisand the elements of its documentationObjective, which explains the purpose of the analysis and explains why it is significant, possibly includingHypotheses, which are potential explanations which you intend to testLiterature Review, which identifies the key pieces of existing research relevant to the project and the hypotheses you have advanced Data Sources, which identify and explain the data used.Analysis and Methodology, which explains the methodology applied to the data.Results and Discussion, which describes your main research findings, whether or not your hypotheses were upheld, and any potential problems with your interpretation of the resultsConclusions, which discusses the implications of your finding relative to your initial project objective.References, which provides standard format citations for all resources drawn upon for the project.

For more detail, go to:http://www.utdallas.edu/~briggs/poec6389/gisc6389_contents.doc

Literature ReviewAll research and analysis builds upon the existing base of scientific knowledgeIt is imperative that you identify the existing state of knowledge in order to Establish appropriate objectivesAdvance meaningful hypothesesSelect and use legitimate methodologies This is accomplished by reviewing the existing literature On scientific knowledgeOn best practices by other organizations

Doing a Literature ReviewDoing a standard Google search is not sufficient! Instead, use Google Scholar http://scholar.google.com/

If you access Google Scholar from on-campus via the UTD Library web page at http://www.utdallas.edu/library/it will give you automatic access to materials subscribed to by UTD library (very clever!)

For information on how to configure Google Scholar to access UTD library materials from off-campus, go tohttp://www.utdallas.edu/library/howto/GoogleScholarPage.htmThis site also gives guidelines on when to use bibliographic databases in place of Google Scholar

Databases available at UTD for literature searches, covering both citations and complete text, can be found at:http://www.utdallas.edu/library/collections/dbases.htm

The single most commonly used bibliographic database is probably Web of Science athttp://www.utdallas.edu/library/collections/dbUZ.htmOr directly athttp://isi10.isiknowledge.com/portal.cgi?DestApp=WOS&Func=Frame

For information on accessing these library databases from off-campus, go to:http://www.utdallas.edu/library/howto/access.htm Because of licensing restrictions, you will need to follow these instructions for off-campus access

How to Format CitationsIt is important that you learn to use the correct format when citing literatureDoing a copy/paste of a URL, which may be gone tomorrow, is not sufficient!The Chicago Manual of Style is the accepted norm.The Chicago Manual of Style. Chicago: University of Chicago Press, 15th ed., 2003 Or replicate the format used by any mainline GIS journalA nice summary is available at:http://www.libs.uga.edu/ref/chicago.html Or, http://library.osu.edu/sites/guides/chicagogd.php Use it!!!!