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Geog 458: Map Sources and ErrorsOutlines1. Importance of data editing2. Detecting errors in a single datasetNodeNode errorsDisplaying potential node errorsSlide 8Polygon errorsAttribute errorsChecking topology errors in geodatabase3. Combining data of different sourcesTransformationRubber-sheeting4. Metadata Content Standard Section 2: Data QualityData Quality ComponentsQuestionsGeog 458:Geog 458:Map Sources and Map Sources and ErrorsErrorsJanuary 20, 2006January 20, 2006Data Storage and EditingData Storage and EditingOutlinesOutlines1.1.IImportance of data editingmportance of data editing2.2.Detecting and editing different types Detecting and editing different types of errorsof errors1)1)EEntity errorsntity errors2)2)Attribute errorsAttribute errors3.3.Combining data of different sourcesCombining data of different sources1)1)TransformationTransformation2)2)Rubber-sheetingRubber-sheeting4.4.Metadata content standardsMetadata content standards1. Importance of data 1. Importance of data editingeditingDData input necessarily involves diverse errorsata input necessarily involves diverse errorsPrimary data capturePrimary data capture: positional accuracy of GPS receivers, : positional accuracy of GPS receivers, geometric distortion of air photo, malfunction of electronic geometric distortion of air photo, malfunction of electronic scanners scanners Secondary data capture: a map in itself the model of reality; Secondary data capture: a map in itself the model of reality; digitizing with no proper use of editing tool (e.g. snapping), digitizing with no proper use of editing tool (e.g. snapping), vectorization without postprocessing, georeferencing with vectorization without postprocessing, georeferencing with imprecise control pointsimprecise control pointsData transfer: information loss caused by (1) file conversion (2) Data transfer: information loss caused by (1) file conversion (2) lack of communication (no metadata) (3) ignorance of GIS userslack of communication (no metadata) (3) ignorance of GIS usersData editing can determine whether to cut off chains of Data editing can determine whether to cut off chains of imperfection (from data input, to analysis, and decision-imperfection (from data input, to analysis, and decision-making)making)Data editing is the pData editing is the process for detecting and eliminating rocess for detecting and eliminating errors inherent in data input, and avoiding error-prone errors inherent in data input, and avoiding error-prone analysis that may lead to wrongfully informed decisionanalysis that may lead to wrongfully informed decision2. Detecting errors in a 2. Detecting errors in a single datasetsingle datasetReading (DeMers chapter 6) Reading (DeMers chapter 6) distinguishes between entity (spatial) distinguishes between entity (spatial) and attribute (non-spatial) errorsand attribute (non-spatial) errorsEntityEntity errors errors Node errors: dangling nodes, pseudo nodesNode errors: dangling nodes, pseudo nodesPolygon errors: sliver, incorrect label pointPolygon errors: sliver, incorrect label pointAttribute errorsAttribute errorsIIncomplete valuesncomplete valuesIncorrect valuesIncorrect valuesNodeNodeWhat is node?What is node?A node is an endpoint of an arc. The A node is an endpoint of an arc. The from-node is the first vertex in the arc; from-node is the first vertex in the arc; the to-node is the last vertex. Arc-node the to-node is the last vertex. Arc-node relation defines connectivityrelation defines connectivityNode typesNode typesNormalNormalDanglingDanglingPseudoPseudoNode errorsNode errorsDangling and pseudo nodes often identify automation Dangling and pseudo nodes often identify automation errors; however they can also be valid components of a errors; however they can also be valid components of a featurefeatureDangling node, if not legitimate (e.g. cul-de-sac) may indicate Dangling node, if not legitimate (e.g. cul-de-sac) may indicate errorserrorsPseudo node, if not legitimate (e.g. island, attribute change) Pseudo node, if not legitimate (e.g. island, attribute change) may indicate errorsmay indicate errorsHow do I check node errors?How do I check node errors?GIS provides functionalities for labeling potential node errorsGIS provides functionalities for labeling potential node errorsBut most of error detection requires visual inspectionBut most of error detection requires visual inspectionHow do I fix node errors?How do I fix node errors?Interactive editing in a proper snapping environment: Editor Interactive editing in a proper snapping environment: Editor toolbartoolbarAutomated data cleaning with a reasonable tolerance level: Automated data cleaning with a reasonable tolerance level: Topology toolbarTopology toolbarDDisplaying potential isplaying potential node errorsnode errorsPseudo nodesPseudo nodesDangling nodesDangling nodesNode errorsNode errorsWWhy do I have to fix node errors? hy do I have to fix node errors? Because it ensures correct topology Because it ensures correct topology that forms the basis for further analysisthat forms the basis for further analysisIIt validates connectivity t validates connectivity If the data is used for network operations such If the data is used for network operations such as hydrological model or routingas hydrological model or routingIIt validates contiguityt validates contiguityIIf the data is used for spatial overlay such as f the data is used for spatial overlay such as point-in-polygon, intersection between line and point-in-polygon, intersection between line and polygonpolygonPolygon errorsPolygon errorsMost common polygon errorsMost common polygon errorsMMissing or multiple label points in arc/info coverageissing or multiple label points in arc/info coverageSSliver polygonliver polygonHow do I identify polygon errors?How do I identify polygon errors?Label error: labelerrors in arc/info workstationLabel error: labelerrors in arc/info workstationSliver polygon: select areas where its aSliver polygon: select areas where its area is less rea is less than reasonably small valuethan reasonably small valueHow do I fix polygon errors?How do I fix polygon errors?Label error: createlabels in arc/info workstationLabel error: createlabels in arc/info workstationSliver polygon: merge silver polygon to neighboring Sliver polygon: merge silver polygon to


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DePaul GEOG 458 - Lecture Notes

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