@2007 Austin Troy
Lecture 4: An Introduction to the Vector Data Model and Map
Layout Techniques
Introduction to GIS
By Brian VoigtUniversity of Vermont
Thanks are due to Dr Troy and Dr Zhou, upon whose lecture much of this material is based.
@2007 Austin Troy
1. Vector Data Model
Introduction to GIS
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• Three basic “feature” or “object” types– Point
– Arc
– Polygon
• A layer holds a single feature type
Reviewing Vector Data Types
Introduction to GIS
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• Attribute table
• Attribute types– Nominal attributes: descriptive information– Ordinal attributes: rank order or scale– Interval/ratio attributes: numeric items, order,
magnitude of difference
Reviewing Vector Data Types
Introduction to GIS
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Point Feature• A point layer: a collection of records with (x,y) coordinates
Introduction to GIS
Image modified from ESRI Arc Info electronic help
0 1 2 3 4 5 60
1
2
3
4
5
6
2,2
6,3
5,5
3,6
1
2
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ID X,Y Coordinat
es1 2,2
2 3,6
3 5,5
4 6,3
…
10 4,1
4,110
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Line (Arc) Feature• One or several line segments define an arc (straight or curved)• 2 points define a line segment• Line endpoints are nodes; angle points are vertices (sing. vertex)• Arcs meet at nodes• Feature is the ARC, not the line segments• Feature has length but not area
Introduction to GIS
Image modified from ESRI Arc Info electronic help
Line segment
Node
Vertices
Node
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Line (Arc) Feature• Each point has a unique location
Introduction to GIS
@2007 Austin Troy
Polygon Feature• Area of homogenous phenomena • In a polygon layer, lines (arcs) define areas• Closed region – first and last coordinate pairs are in the
same location• Line segments bound the polygon
Introduction to GIS
Lines (Arcs)
Points
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• Definition1: Explicit encoding of spatial relationships between objects: the spatial location of each point, line and polygon is defined in relation to each other
Introduction to GIS
Topology
• Definition2: Topology is a collection of rules and relationships that enables the geodatabase to more accurately model geometric relationships found in the world.
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• Two major purposes
Introduction to GIS
Why Topology
– Allows for powerful analysis tools
– Quality control mechanism
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• Arc-node topology
Introduction to GIS
Types of Vector Topology
• Polygon topology
• Route topology
• Region topology
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• Connectivity analysis
Introduction to GIS
Arc-node & Node Topology
Arc-node Topology Arc-node List
Image source: ESRI Arc Info electronic help
Direction
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Polygon-arc Topology
Introduction to GIS
Polygon-arc Topology
Polygon-arc List
The order does matter!
Image source: ESRI Arc Info electronic help
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• Adjacency
Introduction to GIS
Polygon-arc Topology
External polygon
Image source: ESRI Arc Info electronic help
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Introduction to GIS
Route Topology• Define paths based on series of arcs
Image source: ESRI Arc Info electronic help
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• Ensuring “logical consistency”– Define complex and nuanced rules governing
spatial relationships of features
• Data quality– Single layer quality control– Mutli-Layer quality control
Introduction to GIS
Quality control and topology
@2007 Austin Troy
Introduction to GIS
sliver polygon
does not share a border
• Single layer quality control
Quality control and topology
Dangles
undershoot
overshoot
@2007 Austin Troy
Introduction to GIS
• Multi-Layer quality control: Defining spatial rules between layers
Quality control and topology
– Polygon rules: e.g. Must Be Covered by Feature Class of
• ArcCatalog includes new tools for defining and validating topology rules (Book: Building a geodatabase)
– Line rules: e.g. Must not Self Intersect
– Point rules: e.g. Must be Properly Inside Polygons
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• Say we have the following layers: parcels, sidewalks, right of way boundaries, building footprints, zoning
• Rules for spatial relationships– Lots must be enclosed polygons
– Buildings must be entirely within a lot
– Sidewalks must be outside a parcel polygon and entirely within the public right of way
– Lots must fall entirely within a single zoning class
– All lots must have access to a right of way
Introduction to GIS
Topology rules: Example
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Spaghetti Data Model• Non-topological data model
Introduction to GIS
• Collections of line segments and points– Only stores features’ coordinates
– No real connection, topology or relationships
• Not for spatial analysis
• Generally come from CAD files or digitizing
• Can “clean” these data, using user-defined tolerances
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2. Map Layouts and Cartographic Representation
Introduction to GIS
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Introduction to GIS
Map Composition
Map?X
Map Elements?
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Introduction to GIS
Title
Legend
Neatline
North arrow
Scale bar
Notes
Data frame
Map Composition
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Layouts• Create a map for layout in ArcMap Layout view
View>>Layout view.
Introduction to GIS
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Introduction to GIS
Map Compilation• Geographic features
• Other map elements– Legend
– Title
– North arrow
– Scale bar
– Author
– Neatline
– Source of data
– Other objects…
Introduction to GIS
Map Layout: Map Legend
Introduction to GIS
Insert Legend Title
Map Layout: Map Legend
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Layouts
Introduction to GIS
Give a title, e.g. land use … but not “legend”!
Symbol editing
Legends are edited in the Legends property window: Accessed by double clicking a legend.
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Layouts
Introduction to GIS
Legend editing: Items
Items
Style
Symbol
Introduction to GIS
LayoutsEditing legend item style
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Layouts
Introduction to GIS
Editing legend frame
Frame
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Layouts
Introduction to GIS
Editing legend size and position
Size & Position
Introduction to GIS
Map Layout: North Arrows
Introduction to GIS
Map Layout: Scale Bar
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Layouts: data frame• Create a new view or “data frame” in ArcMap
Introduction to GIS
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ArcMap: data frame• More than one frame can be shown in layout view
Introduction to GIS
Frame 1
Frame 2
Introduction to GIS
Data Frames: Context
Introduction to GIS
Data Frames: Inset maps
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Layouts: data frameAccess and edit data frame properties
Introduction to GIS
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MXD Files
Introduction to GIS
• Mxd files are project files
– Save your layout
– All other preferences
– Data is not included
– With an extension .mxd
• File >> Save (As)
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Layer Files
Introduction to GIS
• Save symbology and settings
• Primarily for saving legend settings
• Opening a layer file will open the data layer with all the preferences saved
• With an extension .lyr
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Layer Files
Introduction to GIS
• Use layer files when you have lots of non-numeric categories
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Layer Files
Introduction to GIS
Create a layer file in ArcMap (also in ArcCatalog)
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Layer Files
Introduction to GIS
Import a layer file’s symbology in properties
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Layer Package Files
Introduction to GIS
• Save symbology and settings AND the data!
• With file extension .lpk
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Layer Package Files
Introduction to GIS
Double-click the file to open in ArcMap or ArcCatalog
