Vector Data Model Chapter 3

Geometric Objects What does the object represent? Point=0 dimension, property of location Line=1 dimensional and has the property of length Area=2 dimensional and has the properties of area and boundary. Basic unit is the point and it’s coordiantes

Line Line is a series of points. Node Vertex Smooth line Straight line

Area Defined by lines Contiguous areas Isolated Overlapped Hole

Map Scale Ratio of map distance to ground distance. 1:24,000 is 1 cm = 24,000 centimeters or 240 meters. More details on 1:24,000 than on 1:100,000 What is the symbology?

Topological Data Structure Point: id, x, y Line: Arc-node list, Arc-coordinate list Arc-node list: Arc#, Fnode, Tnode (direction) Arc-coordinate list: Arc#, x-y coordinates. Polygon: Left/Right list, Polygon/Arc list Left/Right list: Arc#, Lpoly, Rpoly Polygon/Arc list: Polygon#, Arc#

Digitization Digitizer Undershoot Overshoot Build/Clean (create topology)

Non-topological Vector Data Computer Aided Design (CAD) .dxf or .dgn etc Shapefile (ArcView .shp = spatial data (geometry) .shx = index for the .shp .dbf = attribute data

Higher-Level Objects Triangulated irregular network (TIN) Delaunay triangulation – iterative process of connecting points with their two nearest neighbors to form triangles as equiangular as possible. x, y, and z values (derived slope and aspect) Sample points Triangle#, number of adjacent, plus points, lines and attribute data

Higher-Level Objects Regions Simple lines and areas Region layers (regions with same attributes) and regions Overlap and/or disconnected/disjoint Subclass of polygon coverage. Region-polygon list: Region#, Polygon# Region-arc list: Region#, Ring#, Arc#

Higher-Level Objects Dynamic Segmentation Sections: arcs of a line coverage Routes: collection of selections that represent linear phenomena Events: attributes connected with dynamic segmentation Section Table, Route Table, Point Event Table, Linear Event Table (more in ArcView presentation)

Object-Oriented Data Model Structural Aspects of Objects Grouping: association, aggregation, generalization, instantiation, and specialization Behavioral Aspects of Objects Inheritance, encapsulation, polymorphism.

Spatial Data Concepts Map scale Spatial resolution (instrumentation) Spatial data accuracy Location accuracy Precision

Topology Arc/Info Connectivity: Arcs connect to each other at nodes Area definition: An area is defined by a series of connected arcs Contiguity: Arcs have directions and left and right polygons. Similar to TIGER