GIS Data Model

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GIS Data Models

Vector Data Models

Vector File Formats

Raster Data Models

Raster File Formats

Lecture 2-3, Jan. 26 and 28, 2004



Data Abstraction

• To use GIS the real world must be

abstracted into points, lines, polygons,

raster cells, and attribute values

• Class examples may use common object

that most people will understand. If you

understand how to abstract common

objects you will be able to apply the samemethod to object in your field



What is Vector Data

• Vector Data uses Points and their (X,Y)

coordinates to represent spatial features

• Points, Lines and Polygons



Points

• A point is a 0 dimensional object and has

only the property of location (x,y)

• Points can be used to Model features such

as a well, building, power, pole, sample

location ect.

• Other name for a point are vertex, node, 0-

cell



Lines

• A line is a one-dimensional object that has the

property of length

• Lines can be used to represent road, streams,

faults, dikes, maker beds, boundary, contactsetc.

• Lines are also called an edge, link, chain, arc, 1-

cell

• In an ArcInfo coverage an arc starts with a node,

has zero or more vertices, and ends with a node



Figure 4.3 p58 Bernhardsen



Polygons

• A polygon is a two-dimensional object with

properties of area and perimeter

• A polygon can represent a city, geologic

formation, dike, lake, river, ect.

• Other name for polygons face, zone 2-cell

• Scale matters





Data Abstraction Discussion

• If you do not understand this the rest of

GIS will not make sense

• Scale Matters

• Intended use Matters



Examples

• Trees

• Dikes

• Roads• Rivers



Topology

• A set of rules on how objects relate to

each other

• Major difference in file formats

• Higher level objects have special topologyrules



Topology Definition

• The Science of mathematics of relationships

used to validate the geometry of vector entities,

and for operations such as network tracing and

tests of polygon adjacency.

• The study of geometric properties that do not

change when the forms are bent, stretched or

under go similar geometric transformations.



Figure 2-9 GIS Fundamentals, Bolstad



Planer Enforcement



Why Topology Matters

• Error Detection

open polygons

unlabeled polygonsslivers

polygons that cannot exist next to each

other • Network Modeling



Show Placitas

• Arc Node Topology

– Cover#

– Lpoly# and Rpoly#

– Tnode fnode

• Label errors



Higher Level Object

• Regions

• Networks

• TIN – Triangulated irregular network• Dynamic Segmentation



Regions

Overlapping areas with different attributes

Fire history

Disconnected areas with the same attributesHawaii



Networks

• Road systems, power grids, water supply

sewerage systems, drainage network

• Continuous connected networks

• Rules for displacement in a network

• Attribute value accumulations due todisplacements



TIN

• Vector Surface Model

• Triangulated Irregular Network

• A set of nonoverlapping triangles eachwith a constant gradient

• A TIN can honor original input elevations



Dynamic Segmentation

• Combines a line coverage with a linear

reference system

• Has event tables for point events and

linear events



Fig 3.13 p52 Chang



Examples and Demo



Shape Files

• Nontopological

• Advantages no overhead to process

topology

• Disadvantages polygons are double

digitized, no topologic data checking

• 3 files .shp .shx .dbf



Coverages

• Original ArcInfo Format

• Directory With Several Files

• Database Files are stored in the InfoDirectory

• Uses Arc Node Topology

– Planer Enforcement – Connectivity

– Adjacency



GeoDatabase

• New GIS Format at ArcGIS 8.0

• Two Types

– Personal Geodatabase – Microsoft access 2000 database

– SDE GeoDatabase – Multi-user

– Can connect to many RDBMS

• Oracle, SQL server, Informix

• File are stored in the format native to the RDBMS



Box 3.5 Geographic Information

Systems, Chang 04 p. 55



GeoDatabase

• Shapes are similar to shape files

• Object-oriented model not a Geo-relational

• There are 25 topology rules than can beused to relate different layers



Raster Data Model

Fi 3 1 G tti St t d ith



Figure 3:1 Getting Started with

Geographic Information Systems,

Clarke (2003) p. 91



Grid Properties

• Each Grid Cell holds one value even if it is empty.

• A cell can hold an index standing for an attribute.

• Cell resolution is given as its size on the ground.

• Point and Lines move to the center of the cell.

• Minimum line width is one cell.

• Rasters are easy to read and write, and easy to

draw on the screen.







Raster Pyramids

• With out pyramids the entire raster must

be read for each screen draw

• Pyramids store reduced resolution dataset

files .rrd to increase the speed of screen

draws

• When you add a raster to ArcMap if

pyramids do not exist you can create them



Raster Resampling

• Nearest Neighbor

– Closest cell

– Continuous and Discrete data

• Bilinear interpolation – Average of nearest 4 cells

– Continuous data only

• Cubic Convolution – Average of nearest 16 cells

– Continuous data only



Quad Tree Compression

• May be use to get variable resolution for

imagery in the National Map



Figure 4.35 Geographic Information Systems and Introduction,

Bernhardsen (2001), p. 87



C. Dana Tomlin, Geographic Information Systems and Cartographic

Modeling (1990), P. 44

• “Yes raster is faster, but raster is vaster,

and vector just seems more corrector”



Images are a form of raster data

• ArcGIS can use many common image

formats











Industry Standard Data Models

• Some Industries have created standard

data models

• It is a good idea to use a standard model

to promote sharing of data

• Some data models can be very complex

• Complex models require custom tools to

be useful





References

• Getting Started with Geographic Information

Systems 4th Edition, Clark (2003)

• Geographic Information Systems an Introduction

3rd Edition, Bernhardsen (2002)• Introduction to Geographic Information Systems

2nd Edition, Chang (2004)

• GIS Fundamentals, Bolstad (2002)

• ArcGIS 8.3 Desktop Help

• Using GRID with ArcInfo version 7 ESRI

Documents

GIS Data Model