Geodatabase Topology

Geodatabase TopologySteven Gay, GISPBoone County Planning Commissionwww.boonecountygis.com

1BackgroundSome complex spatial operations produced odd/unexpected results. Some of the problems were traced back to imprecise geometry (slight overshoots, gaps, slivers, dangles. etc).Planning began in the Spring of 2011, and design work kicked off in August 2011. The first working version was put in place in our production environment in October 2011. ESRIs Geodatabase Xray tool was extremely helpful with quickly making changes to the schema. Refinement of the topology has occurred incrementally, with each iteration building on lessons learned from previous enhancements.Changes to data model and editing workflows werent overwhelming, but did take some getting used to.2What is Topology?Branch of mathematics that deals with spatial relationships between geometric shapesA way to assure geometric coincidence among point, line, and polygon featuresInvolves an in-depth analysis of the coordinate locations and vertices of features stored in a GIS. Includes software logic that tests the integration of feature coordinates/vertices against user-defined business rules which dictate how shapes in a GDB should relate to one anotherTechnical DefinitionShort GIS DefinitionLonger GIS Definition3Why Implement Geodatabase Topology?GIS is all about graphic shapes, so using topology to study the spatial relationships between shapes is only natural.Help ensure and promote GIS data integrity and the accuracy of conclusions drawn from the GIS Avoid common problems often encountered when spatially analyzing non-topological data.Leverage built-in software logic to alert users to data input errors as the data gets edited; thereby making data management/production more efficient, accurate and reliable.4Why Implement Topology?Performing unions between feature classes (e.g. constructing tax district polygons from city, fire and school district feature classes)Enforcing regulations (e.g. zoning districts must follow parcel boundaries)Generating accurate reports (e.g. create a street index table from the centerline feature class)Ensure appropriate resource allocations (e.g. Police Beat polygons must be nested within Police Emergency Service Zone polygons, which must in turn be nested within Law Enforcement Jurisdiction boundary polygons)Examples5Topology BenefitsAllows maintenance of addresses in one location - the Address Point feature class. The address attribution that is published with Parcel polygons and Building polygons originates from the Address point feature class, and topology ensures that all Parcels and Buildings will contain the correct address attribution.Ensures that administrative boundaries (cities, fire districts, school districts, etc.) are aligned with referenced features from other GIS layers, which promotes accuracy and confidence in overlay analyses.Validates attribute coding for Parcel and Subdivision subtypes. This helps ensure compliance with zoning regulations and provides an easy view of variances. Eliminating gaps and overlaps promotes confidence in areal calculations.Parcels can be maintained at the unique deed level. Disallowing gaps and overlaps guarantees the accuracy of Tax Parcels created from dissolving the maintained Parcels. 6

Spatial RelationshipsParcelsAddress PointsBuilding FootprintsEdge of PavementHydrographyPolygonsLinesExterior FeaturesCenterlines7Topology Design Considerations8Where to Locate Topology

Topology Object must be created within a feature dataset

Feature dataset must contain all feature classes that will participate in the topology

May have multiple topology objects inside of the same feature dataset; but feature classes may only belong to one topologyTolerance

The maximum distance that two distinct coordinates may be apart and still be considered to be coincident

Used to compare coordinates and vertices to determine if they occupy the same physical location

Used by topology to resolve inexact intersection locations of coordinates

Accept the default10Geodatabase Subtypes

Allows for subclasses of the features within a feature class

Used to categorize your data and apply different properties (defaults, domains, relationships. etc.) to each category

In topologies, subtypes can have different rules and different coordinate ranks11Feature Class Ranking

A topology can support up to 50 ranks to which feature classes may be assigned

Rankings can take advantage of subtyped feature classes

The lower the rank/number, the less likely features in that rank will shift

Changing the rank of any feature class requires the topology to be revalidated12Core Feature Class Ranks2. Parcels11. Address Points7. Building Footprints9. Pavement13. Hydrography Polygons8. Exterior Features4. Centerlines1. County Boundary3. Subdivisions5. Hydrography Lines6. Administrative Lines10. Recreation Features12. Parks15. Pathways16. School Buildings16. Police Stations16. Liquor Licenses16. Places of Worship16. Day Care Facilities16. Fire Stations16. Medical Care Facilities16. Polling Places16. Food Service Licenses16. Emergency Siren16. Historic Site14. Railroad Lines54,138 features63,130 features67,336 features6,699 features3,417 features83,088 features5,397 features1 feature621 features34,568 features24,224 features1,102 features41 features62,940 features32 features5 features80 features62 features16 features7 features57 features501 features31 features1,436 features80 features409,009 Total Features13Simple vs. Composite TopologyComposite TopologySimple TopologyInvolves only 1 Feature Class

Compares a features shape to itself

Compares a features shape to the shape of another feature from the same feature classInvolves multiple feature classes

Compares a features shape to the shape of another feature from a different feature classESRIs Topology Rules6 Point Topology RulesComposite TopologyMust Coincide Witha point in FC2Each point in FC1Must Be DisjointEach point in FC1------------ separated spatially from other points in FC1Must Be Covered By Boundary OfEach point in FC1a polygon in FC2Must Be Properly InsideEach point in FC1a polygon in FC2Must Be Covered By Endpoint OfEach point in FC1a line in FC2Must Be Covered By LineEach point in FC1in FC2Simple Topology11 Polygon Topology RulesMust Cover Each OtherThe entire area covered by polygons in 2 different feature classesMust Not Overlap Witha polygon in FC2Each polygon in FC1Must Be Larger Than Cluster ToleranceEach polygon in FC1Must Be Covered By Feature Class Of ----------------------- a polygon in FC2Each polygon in FC1Area Boundary Must Be Covered By Boundary OfFC1 polygonspolygons in FC2Must Be Covered ByEach polygon in FC1a polygon in FC2Must Not OverlapEach polygon in FC1another polygon in FC1Must Not Have GapsFC1between its own polygon featuresBoundary Must Be Covered ByFC1 polygonslines in FC2Contains PointEach polygon in FC1-------- at least 1 point in FC2Contains One PointEach polygon in FC1-------- only 1 point in FC2Composite TopologySimple Topology16 Line Topology RulesMust Be Larger Than Cluster ToleranceEach line in FC1Must Not OverlapEach line in FC1another line in FC1Must Not IntersectEach line in FC1another line in FC1Must Not Intersect WithEach line in FC1a line in FC2Must Not Have DanglesEach line in FC1Must Not Have PseudonodesEach line in FC1Must Not Intersect Or Touch InteriorEach line in FC1----------- the interior of another line in FC1Must Not Intersect Or Touch Interior WithEach line in FC1------------------ the interior of a line in FC2Must Not Overlap WithEach line in FC1a line in FC2Must Be Covered By Feature Class OfEach line in FC1----------------------- a line in FC2Must Be Covered By Boundary OfEach line in FC1------------------ a polygon boundary in FC2Must Be InsideEach line in FC1a polygon in FC2Endpoint Must Be Covered ByFC1 linesa point in FC2Must Not Self-OverlapEach line in FC1Must Not Self-IntersectEach line in FC1Must Be Single PartEach line in FC1Simple TopologyComposite TopologyBoone County Core Topology

Simple Polygon TopologyParcel polygons: must not overlap other polygons from the same feature classSubdivision polygons: Building polygons: Exterior Feature polygons: Pavement polygons: Recreation Feature polygons: Park polygons: Hydrography polygons: 3 exceptions62 exceptions

Simple Polygon TopologyParcel polygons: must not have gapsbetween polygons from the same feature class3 exceptions

Simple Point TopologyAddress points: must be disjointSimple Line TopologyAdministrative lines: must not have danglesCenterline lines: must not overlap other lines from the same feature classmust not self-overlapits own shapeHydrography lines: Administrative lines: Pathway lines: must not self-intersectits own shapemust be single partmust not intersect or touch interiorof other lines in the same FC

93 exceptionsOverlapping PolygonsBuilding Footprint polygons: must not overlap an Exterior Feature polygonmust not overlapa Pavement polygonmust not overlapa Recreation Feature polygonExterior Feature polygons: must not overlapa Pavement polygonmust not overlapa Recreation Feature polygonRecreation Feature polygons: must not overlapa Pavement polygonPark polygons: area boundary must be covered by boundary of a Parcel polygon24 exceptions1 exceptions

Confirming Parcel & Subdivision SubtypesSubdivision polygons (Subtype=Single Family): must not overlap a Parcel polygon of subtype Commercialmust not overlap a Parcel polygon of subtype Industrialmust not overlap a Parcel polygon of subtype Mobile Home Parkmust not overlap a Parcel polygon of subtype CommercialSubdivision polygons (Subtype=Multi Family): must not overlap a Parcel polygon of subtype Industrialmust not overlap a Parcel polygon of subtype Mobile Home Parkmust not overlap a Parcel polygon of subtype CondominiumSubdivision polygons (Subtype=Commercial): must not overlap a Parcel polygon of subtype Mobile Home Parkmust not overlap a Parcel polygon of subtype Multi Familymust not overlap a Parcel polygon of subtype SingleFamilymust not overlap a Parcel polygon of subtype CommercialSubdivision polygons (Subtype=Mobile Home): must not overlap a Parcel polygon of subtype Condominiummust not overlap a Parcel polygon of subtype Industrialmust not overlap a Parcel polygon of subtype Multi Familymust not overlap a Parcel polygon of subtype Single Family478 exceptions9 exceptions2 exceptions

Pathway TopologyPathway lines (Subtype=Residential): must not intersect witha Street CenterlinePathway lines (Subtype=Non-Residential): must be insidean Exterior Feature polygon of subtype SidewalkPathway lines (Subtype=Inferred (Driveway)): must not intersect witha Street Centerlinemust be insidean Exterior Feature polygon of subtype DrivewayPathway lines (Subtype=Park): must not intersect witha Street Centerlinemust be insidea Recreation Feature polygon of subtype Walking TrailPathway lines (Subtype=Inferred (Parking Lot)): must not intersect witha Street Centerlinemust be insidea Pavement polygon of subtype Parking LotPathway lines (Subtype=Crosswalk)): must be insidea Pavement polygon of subtype CrosswalkPathway lines (Subtype=Within Roadway)): must be insidea Pavement polygon of subtype Right-Of-Way370 exceptions35 exceptions

Administrative Boundary CoincidenceAdminstrative lines (Subtype=Street Centerline): must be covered bya Street Centerline featureAdministrative lines (Subtype=Hydro Centerline): must be covered bya Hydrography line featureAdministrative lines (Subtype=Parcel Boundary): must be covered bya Parcel polygon boundaryAdministrative lines (Subtype=Subdivision Boundary): must be covered bya Subdivision polygon boundaryAdministrative lines (Subtype=Road Edge of Pavement): must be covered bya Pavement polygon boundaryAdministrative lines (Subtype=County Boundary): must be covered bya County polygon boundary

Address Point Conflation with PolygonsAddress points: must be properly insidea Parcel polygonAddress points (Subtype=Building): must be properly insidea Building polygon of subtype Addressed StructureBuilding polygons (Subtype=Addressed Structure): must contain one pointan Address point of subtype BuildingParcel polygons (Subtype=Acreage): contains pointan Address pointParcel polygons (Subtype=Temporary): Parcel polygons (Subtype=Commercial): Parcel polygons (Subtype=Community): Parcel polygons (Subtype=Industrial): Parcel polygons (Subtype=Mobile Home Park): Parcel polygons (Subtype=Multi Family): Parcel polygons (Subtype=Single Family): Parcel polygons (Subtype=Unknown): contains pointan Address point of subtype BuildingPark polygons: 2 exceptions

Address Point Conflation with PointsFood Service License points: Liquor License points:must coincide withan Address point of subtype BuildingDay Care points:Fire Station points:Historic Site points:Medical Care points:Place Of Worship points:Police Station points:Polling Place points:School Building points:Emergency Siren points:must coincide withan Address point of subtype Other4 exceptions

Changes to the GIS Editing Workflow37Validating Topology

Topology must be validated in order to compile the errorsOnce a feature is edited, its envelope is tagged as a Dirty AreaTopology toolbar allows for topology validation forThe current view extentA user-defined area* Suggest clicking validate current view extent button immediately after performing an edit, and before zooming away from the areaTime it takes to validate will vary based on The number and type of errorsThe geographic extentTolerance settingAll dirty areas must be cleaned to verify if edits conform to topology rules38Topology Toolbar in ArcMap

Map TopologyMap Topology allows you to edit coincident geometry and enforce topology on-they-fly during an edit sessionSpecific topology rules do not come into play. Enforces implied topologyDoesnt persist in the geodatabase. It is saved with the map document.Can be used with features classes or shapefiles housed in the same workspace39Topology Toolbar in ArcMap

GDB TopologyGeodatabase Topology allows you to verify geometry coincidence and visualize errors in a layer. Allows you to specify very specific coincidence rulesTopology persists in the geodatabaseNo setup within editing project requiredRequires periodic revalidation of topology (factors in recent edits and refreshes list of errors)40Fixing Errors in ArcMap

41Fixing Errors in ArcMap

Exceptions can be tagged and will persist in the topology implementation42Fixing Errors in ArcMap

Suggested fixes may provide quick way to correct topology error43Conclusions44