Spatial Data Model: Basic Data Types

2 basic spatial data models exist

vector: based on geometry ofpointslines Polygons

raster: based on geometry ofgrid cells (images, bitmaps, DEMs)

Vector Data

Vector Data ModelPoints: represent discrete point features

airports are point features

each point is stored as a coordinate pair

each point locationhas a record in thetable

Vector Data Model

Lines: represent linear features

roads are linear features

each road segmenthas a record in thetable

Vector Data Model

• Lines start and end at nodes• line #1 goes from node #2 to node #1

• Vertices determine shape of line• Nodes and vertices are stored as coordinate

pairs

node

node

vertex

vertex

vertex

vertex

Vector Data Model

Polygons: represent bounded areas

each bounded polygonhas a record in thetable

landforms and water are polygonal features

Vector Data Model

Points are discreet

Nodes

Vertices

Lines

Nodes

Vertices

Arcs

Closed area (Lines + points ) = polygons

Vector Data Model

Vector data formats available in ArcGIS

ESRI GeoDatabasesESRI shapefilesArcInfo coverages and librariesCAD files (AutoCAD DWG, DXF; microstation DGN)StreetMap filesSpatial Database Engine (SDE) dataASCII point coordinate dataLinear measure (route) data

Vector Data Model

ESRI Geodatabases

Geodatabase can store many files from many source formats

1st preferred vector format in ArcGIS

Rapid display

Fully editable (coordinate and tabular) in ArcGIS

Convenient storage format

Data sets are either point or line or polygon

Vector Data Model

ESRI shapefiles

2nd preferred vector format in ArcGISRapid displayFully editable (coordinate and tabular) in ArcGISSimple in structure

Do not use arc-node topology“Connected” lines do not necessarily share a common nodeAdjacent polygons do not share common bounding arcs

Data sets are either point or line or polygon

Vector Data Model

• less complex data model• polygons do not share bounding lines

Shapefile polygon spatial data model

Vector Data Model

ArcInfo coverages

Commonly found format (due to ArcInfo market dominance)

Data model more complex

Display more slowly in ArcGIS

Coordinate data not editable in ArcGIS

Polymorphic (point/line/polygon/route/annotation/…)

Problematic OS file structure

Vector Data Model

• polygons share bounding lines• same topological rules can be built into

Geodatabase

ArcInfo coverage spatial data model

ASCII coordinate data

Easy to obtain from a variety of sourcesGPSTraverse (survey)Direct reading

OS and application independent

Vector Data Model

Vector Data Model

Characteristics + Features are positioned accurately

+ Shape of features can be represented correctly

+ Features are represented discretely (no fuzzy boundaries)

– Not good for representing spatially continuous phenomena

– Potentially complex data structure (especially for polygons);

- can lead to long processing time for analytical operations

Raster Data

Raster Data Model

origin is set explicitly

cell size is always known

cell references (row/column locations)are known

cell values are referencedto row/column location

values represent numerical phenomena orindex codes for non-numerical phenomena

Raster Data Model

• digital orthophoto

• digital elevation model (DEM)

A few different types of raster data

Raster Data Model

Characteristics:

Rectangular grid of square cells

– Shape of discrete polygonal features generalized by cells

+ Continuous (surface) data represented easily

+ Simple data structure

Raster Data Model

Good at representing continuous phenomena, e.g.,

Wind speed

Elevation, slope, aspect

Chemical concentration

Likelihood of existence of a certain species

Electromagnetic reflectance (photographic or satellite imagery)

Ecological Applications: Vol. 17, No. 2, pp. 508–526.

LINKING OCCURRENCE AND FITNESS TO PERSISTENCE: HABITAT-BASED APPROACH FOR

ENDANGERED GREATER SAGE-GROUSE

Cameron L. Aldridge and Mark S. Boyce

Well_dst 10m cont. distance to nearest standing energy well

Rd_dst 10m cont. distance to nearest road

SB 10m cont. % sagebrush cover determined from a.p.

Crop_dst 10m cont. distance to nearest cultivated land

pCrop 10m cont. prop. of crop in a 1-km moving window

Homework

Read “getting data into ArcGIS Maps”, “displaying layers”, “changing layer display properties”, “project and data management”, “sample data”, “data export”

Assignment 2. “Introduction to GIS” (due January 22)