NR 322: Raster Analysis I

Jim GrahamFall 2008Chapter 7

Types of Rasters• Land Cover: forest, grass, water, roads,

urban• Digital Elevation Model: DEM• Aerial Photos• Satellite Photos• Scanned: DRG, 24k Topos• Derived rasters: lots!

Derived Rasters• Land Cover from satellite and

aerial• Topography: Slope, aspect,

hillshade• Ecoregions• Suitable Habitat• Flood plains• Geological Regions

Raster To Vector• Satellite & Aerial

– Land Cover: roads, forests, etc.– Buildings

• DEMs– Contours– Peaks & Valleys– Stream Networks– Watersheds

Vector To Raster• Drawing!• Points of interest• Roads• Water bodies• Contours

GIS Analysis

AnalysisResults

Raster toVector

Vector toRaster

Raster Analysis• Topography: Slope, aspect, contours• Raster Math• Statistics: min, max, mean, std. dev.• Distance• Density• Interpolation• Classification• Raster / Vector Conversions

Raster Math• A matrix of pixels

12 20 23 34 40

15 23 30 31 39

15 22 29 30 40

14 20 28 29 38

13 19 25 32 37

Columns

Rows

Spatial Analyist

Analysis Environment• Spatial Reference (Coordinate System)

– Make them the same• Extent

– Area of interest– All rasters should overlap

• Cell Size– Largest of all rasters or larger

Spatial Analyst: General

Spatial Analyst: Extent

Spatial Analyst: Cell Size

Raster Calculator

Raster Math

1 22 3

12 9

13 10

13 11

15 13+ =

+ =1 12 13

Common Functions• Local:

– Arithmatic: +,-,/, *, • MOD (Modulo): returns the remainder

– Boolean: • OR: If either input is true, output is true• AND: If both inputs are true, output is true

– CON (Conditional)

Mathematical Functions• Abs (absolute): flips negatives to positive• Ceil (ceiling): float to integer next highest

integer value (i.e. 1.1 -> 2)• Floor: float to integer giving next lowest

integer value (i.e. 1.1 -> 1)• Int (integer): truncates float to integer

Exponents• Exp()• Exp10()• Ln()• Log10()• Max()• Min()• Pow()• SetNull()• Sqrt()• Sum()

Comparisons• <> (Not Equals)• == (Equals)• < (Less than)• <= (Less than or equal to)• > (Greater than)• >= (Greater than or equal to)

Raster Math: Comparisons

1 22 3

2 2

3 2

0 0

0 1> =

> =1 2 0

Raster Math: Boolean AND

0 01 1

0 1

0 1

0 0

0 1AND =

AND =0 1 0

“AND” works but the calculator will insert “&”

Raster Math: Boolean OR

0 00 1

1 1

0 1

1 1

0 1OR =

OR =0 1 1

“OR” works but the calculator will insert “!”

Conditional Operator• Con(<condition>,<true>,<false>)• Given a raster “condition”:

– Puts the true value where true and false value where false

• Example:– Find the elevations in Rocky over 3000

meters– HighElevations=con(RockyDEM>3000,1,0)

Elevations over 3000 meters

Elevations over 3000 meters