Geog 405: Advanced Spatial Analysis © J.M. Piwowar1Spatial Data Models Characteristics of Raster Data Longley et al., 2001. Geographic Information Systems.

© J.M. Piwowar 1Geog 405: Advanced Spatial Analysis Spatial Data Models

Characteristics of Raster Data

Lon

gley

et a

l., 2

001.

Geo

grap

hic

Info

rmat

ion

Syst

ems

and

Scie

nce.

Wile

y.

© J.M. Piwowar 2Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Spatial Data Models

How do we represent spatial information in a computer?

The rules to convert real geographical variation into discrete objects.

© J.M. Piwowar 3Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Spatial Data Models

© J.M. Piwowar 4Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Spatial Data Models

Dav

is, B

.E.,

2001

. GIS

: A

Vis

ual A

ppro

ach

(2nd

ed.

). A

lban

y, N

Y: O

nWor

d Pr

ess.

© J.M. Piwowar 5Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Spatial Data Models

Aro

noff

, 199

3. G

eogr

aphi

c In

form

atio

n Sy

stem

s: A

Man

agem

ent P

ersp

ectiv

e. O

ttaw

a : W

DL

Pub

licat

ions

.

© J.M. Piwowar 6Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

The Vector Data Model

Feature Representationpoints

vertices nodes label points

lines lines arcs

areas polygons  

Dav

is, B

.E.,

2001

. GIS

: A

Vis

ual A

ppro

ach

(2nd

ed.

). A

lban

y, N

Y: O

nWor

d Pr

ess.

© J.M. Piwowar 7Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

The Raster Data Model

Feature Representationall geographic features -

points, lines, areas - are represented by grid cells

grid resolution - the minimum linear dimension of the smallest unit of geographic space sampled

Dav

is, B

.E.,

2001

. GIS

: A

Vis

ual A

ppro

ach

(2nd

ed.

). A

lban

y, N

Y: O

nWor

d Pr

ess.

© J.M. Piwowar 8Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Raster Data Layers

Lo

& Y

eung

, 200

2. C

once

pts

& T

echn

ique

s of

Geo

grap

hic

Info

rmat

ion

Syst

ems.

Pre

ntic

e-H

all.

© J.M. Piwowar 9Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

The Raster Data Model

http

://w

ww

.aw

i-br

emer

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/GE

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arin

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iple

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Field representation Object representation

© J.M. Piwowar 10Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Raster Resolution

30 m resolution

3 m resolution

0.6 m resolution

© J.M. Piwowar 11Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Raster Resolution

Dav

is, B

.E.,

2001

. GIS

: A

Vis

ual A

ppro

ach

(2nd

ed.

). A

lban

y, N

Y: O

nWor

d Pr

ess.

© J.M. Piwowar 12Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Raster Resolution

30 m resolution

625 cells3 m resolution62,500 cells

© J.M. Piwowar 13Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Raster Advantages

Dav

is, B

.E.,

2001

. GIS

: A

Vis

ual A

ppro

ach

(2nd

ed.

). A

lban

y, N

Y: O

nWor

d Pr

ess.

© J.M. Piwowar 14Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Raster Disadvantages

Dav

is, B

.E.,

2001

. GIS

: A

Vis

ual A

ppro

ach

(2nd

ed.

). A

lban

y, N

Y: O

nWor

d Pr

ess.

© J.M. Piwowar 15Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Vector Advantages

Dav

is, B

.E.,

2001

. GIS

: A

Vis

ual A

ppro

ach

(2nd

ed.

). A

lban

y, N

Y: O

nWor

d Pr

ess.

© J.M. Piwowar 16Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Vector Disadvantages

Dav

is, B

.E.,

2001

. GIS

: A

Vis

ual A

ppro

ach

(2nd

ed.

). A

lban

y, N

Y: O

nWor

d Pr

ess.

© J.M. Piwowar 17Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Vector vs. Raster

Vector the location of

each vertex needs to be stored explicitly

sparse partitioning of geographic space

Raster the geographic

location of each cell is implied by its position in the cell matrix

complete partitioning of geographic space

© J.M. Piwowar 18Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Vector vs. Raster

Vectorprovides for

precise positioning of features in geographic space

intuitive representation of geographic space

Raster the cell size

determines the resolution at which the data are represented

linear features are hard to represent

© J.M. Piwowar 19Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Vector vs. Raster

Vectormore difficult to

understand

some types of analysis can be difficult

Rasterconceptually

simple data structure

raster algorithms are often simpler and faster

© J.M. Piwowar 20Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Vector vs. Raster

Vectorcompact file sizes

very large vector databases have been built for a variety of purposes

Raster large file sizes

much new data come from remote sensing image analysis

© J.M. Piwowar 21Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Spatial vs. Temporal Resolution

Vis

ual L

earn

ing

Syst

ems,

200

3.

© J.M. Piwowar 22Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Spatial vs. Temporal Resolution

Vis

ual L

earn

ing

Syst

ems,

200

3.

0.62 m resolution; 2002

30 m resolution; 2000

© J.M. Piwowar 23Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Raster Attributes

Lo

& Y

eung

, 200

2. C

once

pts

& T

echn

ique

s of

Geo

grap

hic

Info

rmat

ion

Syst

ems.

Pre

ntic

e-H

all.

© J.M. Piwowar 24Geog 409: Advanced Spatial Analysis & Modelling Spatial Data Models

Common Raster Data Formats

TIFF (Tagged Image File Format)

JPEG (Joint Photographic Editors Group)

GIF (CompuServe Graphics Interchange Format)

MrSID (Multi-resolution Seamless Image Database)

BIL (ERDAS Band-Interleaved-by-Line Format)

IMG (could be any type of image)