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Continuous vs. Categorized
• Continuous:– Like photographs– Satellite and aerial photos– Best for analysis
• Categorized or discrete– Land Cover– Eco-regions– Limited analysis– Careful on precision and accuracy
“No-Data” or NULL Values
• Rasters are always rectangular
• No-Data values are “transparent” and are not used for calculations
Geo-Referenced Raster
• Known Projection and Datum
• Width and height of a pixel in map units
(X1,Y1)
Width in Pixels
Height in pixels
Geo-Referenced Raster
• Known Projection and Datum
(X1,Y1)
(X3,Y3)
Types of Rasters
• Digital Elevation Model (DEM)
• Digital Raster Graphic (Topos)
• Satellite and Aerial Photos
• Land Cover & other natural characteristics
• Cost Distance & other economic
• Population, taxes, etc.
• Your own!
Aspect – Direction of the slope
Slope
Aspect (Direction)
Angle
Rise
Run
Slope = (Rise/Run) * 100%
Creating a Hillshade
• Obtain a DEM
• Crop to Desired Area
• Create Hillshade
• Apply color ? To DEM
• Add DEM over Hillshade with Transparency
• Screen shots:– Hillshade dialog– Colorizing dems– Transparency
Spatial Analyst Extension
• Make sure “Spatial Analyst” is Checked
Tool Bar
• Right-click in the menu area
• Select “Spatial Analyst”
Hill-shading
• Azimuth: “Direction” of the sun relative to the ground. 0 is north.
• Altitude: Angle from the horizon to the sun.
North
Azimuth
Altitude
Horizon
Continuous vs. Categorized
• Continuous:– Like photographs– Satellite and aerial photos– Best for analysis
• Categorized or discrete– Land Cover– Eco-regions– Limited analysis– Careful on precision and accuracy
“GeoReferenced” File Formats
• GRID: ESRI’s format
• GeoTIFF: Excellent support
• MrSID: LizardTech
• IMG: ERDAS
• ECW: ERMapper
• BIL, BIP, BSQ: See header (w/prj)
• “ASCII” or “GRID ASCII” (w/prj)
World Files
• Contains:– X-dimention Pixel size in map units– Y-axis rotation– X-axis rotation– Y- dimension Pixel size in map units
(negative)– X-coordinate of upper-left pixel– Y-coordinate of upper-left pixel
• Image file contains width and height
Not Geo-Referenced
• BMP
• PNG
• GIF
• JPEG
• Maybe with a world file and prj file?
JPEG
• Joint Photographic Experts Group
• Widest used photo format
• Not for use with vectors
• JPEG2000– Completely new format!– Can be georeferenced
Edge of Rocky Mountain National Park Boundary with high JPEG compression
Tagged Image File Format
• TIFF• Can be georeferenced (GeoTIFF)
– Can tell in ArcCatalog or ArcMap
• TIFF w/world file– Also need Projection and Datum (prj?)
• Can be compressed– Run-length – Categorical data– LZW – Categorical data– Huffman encoding – Categorical data– JPEG- Continuous data (don’t used on
Categorical data!)
GRIDS
• ESRI’s native raster format
• Pyramids
• Not an exchange format!
ASCII format• NCOLS 10• NROWS 9• XLLCORNER 1000• YLLCORNER 1000• CELLSIZE 1• NODATA_VALUE -9• -9 -9 1 1 0 1 0 1 -9 -9• -9 -9 1 1 2 2 2 1 1 -9• -9 1 1 1 2 2 2 2 3 3 • Etc.• See example
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
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
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 2
2 3
2 2
3 2
0 0
0 1> =
> =1 2 0
Raster Math: Boolean AND
0 0
1 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 0
0 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)
Viewshed
• Shows which “pixels” can be seen from pre-defined locations
