Steven Gay, GISP Boone County Planning Commission

Background Some 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 The first working version was put in place in our production environment in October ESRI’s 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 weren’t overwhelming, but did take some getting used to.

What is Topology? Branch of mathematics that deals with spatial relationships between geometric shapes A way to assure geometric coincidence among point, line, and polygon features Involves 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 another Technical Definition Short GIS Definition Longer GIS Definition

Why 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.

Why 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) Examples

Topology Benefits Allows 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.

Spatial Relationships Parcels Address Points Building Footprints Edge of Pavement Hydrography Polygons Lines Exterior Features Centerlines

Topology Design Considerations

Where 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 topology

Tolerance 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 default

Geodatabase 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 ranks

Feature 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 revalidated

Core Feature Class Ranks 2. Parcels11. Address Points 7. Building Footprints 9. Pavement 13. Hydrography Polygons 8. Exterior Features 4. Centerlines 1. County Boundary 3. Subdivisions 5. Hydrography Lines 6. Administrative Lines 10. Recreation Features 12. Parks 15. Pathways 16. School Buildings 16. Police Stations 16. Liquor Licenses 16. Places of Worship 16. Day Care Facilities 16. Fire Stations 16. Medical Care Facilities 16. Polling Places 16. Food Service Licenses 16. Emergency Siren 16. Historic Site 14. Railroad Lines 54,138 features63,130 features 67,336 features 6,699 features 3,417 features 83,088 features 5,397 features 1 feature 621 features 34,568 features 24,224 features 1,102 features 41 features 62,940 features 32 features 5 features 80 features 62 features 16 features 7 features 57 features 501 features 31 features 1,436 features 80 features 409,009 Total Features

Simple vs. Composite Topology Composite Topology Simple Topology Involves only 1 Feature Class Compares a feature’s shape to itself Compares a feature’s shape to the shape of another feature from the same feature class Involves multiple feature classes Compares a feature’s shape to the shape of another feature from a different feature class

ESRI’s Topology Rules

6 Point Topology Rules Composite Topology Must Coincide Witha point in FC2Each point in FC1 Must Be DisjointEach point in FC separated spatially from other points in FC1 Must Be Covered By Boundary OfEach point in FC1a polygon in FC2 Must Be Properly InsideEach point in FC1a polygon in FC2 Must Be Covered By Endpoint OfEach point in FC1a line in FC2 Must Be Covered By LineEach point in FC1in FC2 Simple Topology

11 Polygon Topology Rules Must Cover Each OtherThe entire area covered by polygons in 2 different feature classes Must Not Overlap Witha polygon in FC2Each polygon in FC1 Must Be Larger Than Cluster ToleranceEach polygon in FC1 Must Be Covered By Feature Class Of a polygon in FC2Each polygon in FC1 Area Boundary Must Be Covered By Boundary OfFC1 polygons’polygons in FC2 Must Be Covered ByEach polygon in FC1a polygon in FC2 Must Not OverlapEach polygon in FC1another polygon in FC1 Must Not Have GapsFC1between its own polygon features Boundary Must Be Covered ByFC1 polygons’lines in FC2 Contains PointEach polygon in FC at least 1 point in FC2 Contains One PointEach polygon in FC only 1 point in FC2 Composite Topology Simple Topology

16 Line Topology Rules Must Be Larger Than Cluster ToleranceEach line in FC1 Must Not Overlap Each line in FC1another line in FC1 Must Not IntersectEach line in FC1another line in FC1 Must Not Intersect WithEach line in FC1a line in FC2 Must Not Have DanglesEach line in FC1 Must Not Have PseudonodesEach line in FC1 Must Not Intersect Or Touch InteriorEach line in FC the interior of another line in FC1 Must Not Intersect Or Touch Interior WithEach line in FC the interior of a line in FC2 Must Not Overlap WithEach line in FC1a line in FC2 Must Be Covered By Feature Class OfEach line in FC a line in FC2 Must Be Covered By Boundary OfEach line in FC a polygon boundary in FC2 Must Be InsideEach line in FC1a polygon in FC2 Endpoint Must Be Covered ByFC1 lines’a point in FC2 Must Not Self-OverlapEach line in FC1 Must Not Self-IntersectEach line in FC1 Must Be Single PartEach line in FC1 Simple Topology Composite Topology

Boone County Core Topology

Simple Polygon Topology Parcel polygons: …must not overlapother polygons from the same feature class Subdivision polygons: Building polygons: Exterior Feature polygons: Pavement polygons: Recreation Feature polygons: Park polygons: Hydrography polygons: 3 exceptions 62 exceptions

Simple Polygon Topology Parcel polygons: …must not have gaps between polygons from the same feature class 3 exceptions

Simple Point Topology Address points: …must be disjoint

Simple Line Topology Administrative lines: …must not have dangles Centerline lines: …must not overlapother lines from the same feature class …must not self-overlap it’s own shape Hydrography lines: Administrative lines: Pathway lines: …must not self-intersect it’s own shape …must be single part …must not intersect or touch interior of other lines in the same FC 93 exceptions

Overlapping Polygons Building Footprint polygons: …must not overlapan Exterior Feature polygon …must not overlap a Pavement polygon …must not overlap a Recreation Feature polygon Exterior Feature polygons: …must not overlap a Pavement polygon …must not overlap a Recreation Feature polygon Recreation Feature polygons: …must not overlap a Pavement polygon Park polygons: …area boundary must be covered by boundary of a Parcel polygon 24 exceptions 1 exceptions

Confirming Parcel & Subdivision Subtypes Subdivision polygons (Subtype=‘Single Family’): …must not overlapa Parcel polygon of subtype ‘Commercial’ …must not overlapa Parcel polygon of subtype ‘Industrial’ …must not overlapa Parcel polygon of subtype ‘Mobile Home Park’ …must not overlapa Parcel polygon of subtype ‘Commercial’ Subdivision polygons (Subtype=‘Multi Family’): …must not overlapa Parcel polygon of subtype ‘Industrial’ …must not overlapa Parcel polygon of subtype ‘Mobile Home Park’ …must not overlapa Parcel polygon of subtype ‘Condominium’ Subdivision polygons (Subtype=‘Commercial’): …must not overlapa Parcel polygon of subtype ‘Mobile Home Park’ …must not overlapa Parcel polygon of subtype ‘Multi Family’ …must not overlapa Parcel polygon of subtype ‘SingleFamily’ …must not overlapa Parcel polygon of subtype ‘Commercial’ Subdivision polygons (Subtype=‘Mobile Home’): …must not overlapa Parcel polygon of subtype ‘Condominium’ …must not overlapa Parcel polygon of subtype ‘Industrial’ …must not overlapa Parcel polygon of subtype ‘Multi Family’ …must not overlapa Parcel polygon of subtype ‘Single Family’ 478 exceptions 9 exceptions 2 exceptions

Pathway Topology Pathway lines (Subtype=‘Residential’): …must not intersect witha Street Centerline Pathway lines (Subtype=‘Non-Residential’): …must be insidean Exterior Feature polygon of subtype ‘Sidewalk’ Pathway lines (Subtype=‘Inferred (Driveway)’): …must not intersect witha Street Centerline …must be insidean Exterior Feature polygon of subtype ‘Driveway’ Pathway lines (Subtype=‘Park’): …must not intersect witha Street Centerline …must be insidea Recreation Feature polygon of subtype ‘Walking Trail’ Pathway lines (Subtype=‘Inferred (Parking Lot)’): …must not intersect witha Street Centerline …must be insidea Pavement polygon of subtype ‘Parking Lot’ Pathway lines (Subtype=‘Crosswalk)’): …must be insidea Pavement polygon of subtype ‘Crosswalk’ Pathway lines (Subtype=‘Within Roadway)’): …must be insidea Pavement polygon of subtype ‘Right-Of-Way’ 370 exceptions 35 exceptions

Administrative Boundary Coincidence Adminstrative lines (Subtype=‘Street Centerline’): …must be covered bya Street Centerline feature Administrative lines (Subtype=‘Hydro Centerline’): …must be covered bya Hydrography line feature Administrative lines (Subtype=‘Parcel Boundary’): …must be covered bya Parcel polygon boundary Administrative lines (Subtype=‘Subdivision Boundary’): …must be covered bya Subdivision polygon boundary Administrative lines (Subtype=‘Road Edge of Pavement’): …must be covered bya Pavement polygon boundary Administrative lines (Subtype=‘County Boundary’): …must be covered bya County polygon boundary

Address Point Conflation with Polygons Address points: …must be properly insidea Parcel polygon Address points (Subtype=‘Building’): …must be properly insidea Building polygon of subtype ‘Addressed Structure’ Building polygons (Subtype=‘Addressed Structure’): …must contain one pointan Address point of subtype ‘Building’ Parcel polygons (Subtype=‘Acreage’): …contains pointan Address point Parcel 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 ‘Building’ Park polygons: 2 exceptions

Address Point Conflation with Points Food Service License points: Liquor License points: …must coincide withan Address point of subtype ‘Building’ Day 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 ‘Other’ 4 exceptions

Changes to the GIS Editing Workflow

Validating Topology Topology must be validated in order to compile the errors Once a feature is edited, it’s ‘envelope’ is tagged as a “Dirty Area” Topology toolbar allows for topology validation for 1)The current view extent 2)A user-defined area * Suggest clicking ‘validate current view extent’ button immediately after performing an edit, and before zooming away from the area Time it takes to validate will vary based on 1.The number and type of errors 2.The geographic extent 3.Tolerance setting All dirty areas must be cleaned to verify if edits conform to topology rules

Topology Toolbar in ArcMap Map Topology Map Topology allows you to edit coincident geometry and enforce topology on-they-fly during an edit session Specific topology rules do not come into play. Enforces “implied topology” Doesn’t persist in the geodatabase. It is saved with the map document. Can be used with features classes or shapefiles housed in the same workspace

Topology Toolbar in ArcMap GDB Topology Geodatabase Topology allows you to verify geometry coincidence and visualize errors in a layer. Allows you to specify very specific coincidence rules Topology persists in the geodatabase No setup within editing project required Requires periodic revalidation of topology (factors in recent edits and refreshes list of errors)

Fixing Errors in ArcMap

Exceptions can be tagged and will persist in the topology implementation

Fixing Errors in ArcMap Suggested fixes may provide quick way to correct topology error

Conclusions