RASTER ANALYSIS S H A W N L. P E N M A N E A R T H D A T A A N A LY S I S C E N T E R U N I V E R S I T Y O F N E W M E X I C O

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1 RASTER ANALYSIS S H A W N L. P E N M A N E A R T H D A T A A N A LY S I S C E N T E R U N I V E R S I T Y O F N E W M E X I C O

2 TOPICS COVERED Spatial Analyst basics Raster / Vector conversion Raster data fundamentals Cells, cell values, zones and regions Basic spatial properties of raster Points, lines, polygons, distance, adjacency, buffer, network Types of raster functions Raster reclassification Raster overlay Raster query and map algebra Distance functions Zonal statistics Other raster analysis tools

3 SPATIAL ANALYST BASICS

4 SPATIAL ANALYST TO WORK WITH RASTER DATA

5 ARCGIS SPATIAL ANALYST Extremely useful extension to ArcGIS Same for all levels (ArcView, ArcInfo) Needs to be purchased separately. Spatial Analyst uses grids essentially makes ArcGIS into a raster program Spatial analysis and modeling tools queries, overlay, distance, proximity, density, slope, aspect, hillshade, viewshed, contours, etc.

6 TURNING SPATIAL ANALYST ON

7 SPATIAL ANALYST TOOLBAR & ARCTOOLBOX ArcMap 10.1 Spatial Analyst & Image Classification Toolbars ArcMap 9.3 Spatial Analyst Toolbar Tools now in ArcToolbox

8 RASTER FORMATS ADRG (ARC Digitized Raster Graphics) CADRG (Compressed ADRG) CIB (Controlled Image Base) DTED (Digital Terrain Elevation Data) ERDAS GIS, LAN, RAW, IMG ERMapper (ERS) BIL, BIP, BSQ ESRI GRID GIF, JPG, SID, TIF, BMP

9 Grids are the main raster format of ArcGIS Spatial Analyst. Output created by Spatial Analyst consist of grids these can be converted to other formats using ArcCatalog. GRIDS

10 WORKING WITH GRIDS Grids are stored very much like coverages. Always set a proper working directory and never delete files manually in Windows Explorer but use ArcCatalog.

11 BUILDING PYRAMIDS Pyramids are used to improve performance. They are a downsampled version of the original raster dataset and can contain many downsampled layers. Each successive layer of the pyramid is downsampled at a scale of 2:1. Pyramids can speed up the display of raster data by retrieving only the data at a specified resolution that is required for the display.

12 SINGLE-BAND RASTERS

13 MULTIBAND RASTERS

14 DISPLAYING GRIDS Grid data files can be classified using the Symboloy properties Grid cells are given a solid color based on cell values Both discrete and continuous data are used discrete data are stored an integer grid theme, e.g. land use, soil type, land ownership, etc. continuous data are stored as an integer or floating point grid theme, e.g. population density, elevation, price of land etc. Various classification methods can be used Unique values Classified Stretched

15 GRID MAP EXAMPLE Housing units in city of Pittsburgh Census block centroids Kernel density raster map GIS TUTORIAL 1 - Basic Workbook

16 UNIQUE VALUES

17 CLASSIFIED

18 STRETCHED

19 ANALYSIS OPTIONS Now settings under Environments

20 ENVIRONMENTS

21 ANALYSIS MASK The mask identifies those cells within the analysis extent that will not be considered when performing an operation or a function. All identified cells will be "out" and assigned to the nodata value on all subsequent output raster datasets.

22 ANALYSIS MASK The analysis extent be a vector or raster file in the example, a vector polygon is used as a mask to create slope map from a DEM but only within the study area.

23 ANALYSIS EXTENT When performing analysis, the area of interest may be a portion of a larger raster dataset. If the area of interest is a portion of a larger raster dataset, the analysis extent can be set to encompass only the desired cells. All subsequent results from analysis will be to this extent. The analysis extent is a rectangle and is specified by identifying the coordinates of the window in map space.

24 RASTER RESOLUTION

25 CELL SIZE The output cell size, or resolution, for any operation or function can be set to any size desired. The default output resolution is determined by the coarsest of the input raster datasets.

26 RASTER / VECTOR CONVERSION

27 RASTER / VECTOR CONVERSION

28 RASTER / VECTOR CONVERSION

29 RASTER / VECTOR CONVERSION

30 RASTER DATA FUNDAMENTALS

31 CELLS, ROWS, COLUMNS AND VALUES Columns (4,1) Rows Raster data sets are an organized matrix of cells. Cells are organized into rows & columns which have an index position number. The top left cell is at the (0,0) position. The notation uses column first, followed by row.

32 Y axis RASTER DATA AND COORDINATE SYSTEMS Raster origin (135,982;1,251,821) Raster data layers are stored with a Cartesian coordinate system. Positions on the grid have real-world locations. Each cell can be referenced by an X,Y location. All cells are square & are the same size. Coordinate origin (0,0) X axis

33 CELL VALUES

34 INTEGER VS. FLOATING POINT

35 DATA TYPES AND CELL VALUES

36 WORKING WITH NO DATA

37 ZONES An example with 6 zones Any two or more cells within the same value belong to the same zone a zone can consist of cells that are connected, disconnected or both.

38 ZONES AND ATTRIBUTE DATA Value Count

39 BASIC SPATIAL PROPERTIES OF RASTER

40 BASIS SPATIAL PROPERTIES IN RASTER Points Line Polygons Distance Adjacency Buffer Network Spatial Coincidence

41 RASTER - POINTS

42 RASTER - LINES

43 RASTER - POLYGONS

44 RASTER - DISTANCE

45 RASTER - ADJACENCY Orthogonal and diagonal Orthogonal only

46 RASTER - BUFFER

47 RASTER - NETWORK

48 RASTER SPATIAL COINCIDENCE

49 TYPES OF RASTER FUNCTIONS

50 RASTER FUNCTIONS Local Zonal Focal Global

51 LOCAL FUNCTION EXAMPLE: RASTER CALCULATOR * 2 =

52 GLOBAL FUNCTION EXAMPLE: STRAIGHT- LINE DISTANCE Distance of =

53 RASTER RECLASSIFICATION

54 RECLASSIFY Reclassifying your data simply means replacing input cell values with new output cell values. The input data can be any supported raster format. If you add a multiband raster, the first band will be taken and used in the reclassification.

55 ELEVATION RASTER

56

57 RECLASSIFY

58 RECLASSIFY There are many reasons why you might want to reclassify your data. Some of the most common reasons are: To replace values based on new information To classify certain values together for display To classify certain values together for conversion to vector format for analysis To reclassify values to a common scale To set specific values to nodata or to set nodata cells to a value

59 RECLASSIFY Reclassification is useful when you want to replace the values in the input raster with new values. This could be due to finding out that the value of a cell or a number of cells should actually be a different value. For example, this may happen if the landuse in an area changed over time. You may want to simplify the information in a raster. For instance, you may want to group together various types of forest into one forest class.

60 RECLASSIFY Another reason to reclassify is to assign values of preference, sensitivity, priority, or some similar criteria to a raster. This may be done on a single raster (a raster of soil type may be assigned values of 1 10 that represent erosion potential) or with several rasters to create a common scale of values. For example, when finding slopes most at risk of avalanche activity, input rasters might be slope, soil type, and vegetation. Each of these rasters might be reclassified on a scale of 1 10 depending on the susceptibility of each attribute in each raster to avalanche activity (that is, steep slopes in the slope raster might be given a value of 10 because they are most susceptible to avalanche activity).

61 RECLASSIFY Sometimes you want to remove specific values from your analysis. This might be, for example, because a certain landuse type has restrictions (such as wetland restrictions), which means you cannot build there. In such cases, you might want to change these values to nodata in order to remove them from further analysis. In other cases, you may want to change a value of NoData to be a value such as in the case where new information means a value of NoData has become a known value.

62 RECLASSIFY

63 RECLASSIFY

64 FTP SITE ftp://edacftp.unm.edu/outgoing/pub/spenman/geog581l/exam ples_raster_analysis/part1

65 DEMO/PRACTICE Open Tutorial1-1 mxd DEM Properties, Source tab how many columns & rows and what is their size? What is the projection? Statistics what is the range of elevation? Examine attribute table of LandUse How many records are there? Set Environment turn on spatial analyst toolbar Set Raster Analysis Environment Cell size, select as specified as below, 50, mask Pittsburgh Extract Land Use using a mask Use layer file to symbolize new land use layer

66 DEMO/PRACTICE Reclassify Tool Reclassify LandUse All developed into one category All forest into one category All wetlands into one category Have to look at classification (symbology tab) to figure out which numbers belong to developed, forest and wetlands categories Examine changes Try reclassify with Classification window Use reclassified LandUse and export to polygon