COMMON GIS TECHNIQUES FOR VECTOR AND RASTER DATA PROCESSING Ophelia Wang, Department of Geography and the Environment, University of Texas
PART I: BASIC VECTOR TOOLS
CLIP A FEATURE BASED ON THE EXTENT OF ANOTHER FEATURE
USE THE UNIQUE VALUES OF A ZONING FEATURE TO SPLIT ANOTHER FEATURE
CREATE A HOLLOW FEATURE
SELECT PORTIONS OF A FEATURE THAT INTERSECTS WITH ANOTHER FEATURE
SELECT PORTIONS OF A FEATURE THAT DOES NOT OVERLAP WITH ANOTHER ONE
SELECT FEATURES BASED ON ATTRIBUTES OR SPATIAL RELATIONSHIP WITH OTHER FEATURES
COMBINE MULTIPLE FEATURES INTO ONE
CREATE BUFFER ZONES OF VARIOUS SIZES AND TYPES AROUND FEATURES
CREATE NOT JUST ONE BUFFER, BUT MULTIPLE BUFFERS.
COMPUTE THE DISTANCE FROM ONE FEATURE TO THE NEAREST FEATURE
COMPUTE THE DISTANCES TO ALL FEATURES
AGGREGATE AND DISSOLVE FEATURES
PART II: COMMON RASTER PROCESSING; MOSAIC MULTIPLE RASTERS TOGETHER
CLIP RASTER BY EXTENT OF A RECTANGLE OR CIRCLE
CHANGE RASTER CELL SIZE AND RESAMPLE THE CELLS
GET CELL VALUES OF PARTICULAR CELLS
A VERY HANDY TOOL TO USE
OR SET THE MASK IN SPATIAL ANALYST S OPTIONS AND THEN CLICK EVALUATE IN RASTER CALCULATOR TO CLIP THE RASTER
EXTRACT THE CELL VALUE OF A RASTER AT WHICH A POINT IS LOCATED
GET THE CELL VALUES OF A RASTER AT THE LOCATIONS OF ANOTHER RASTER/FEATURE
REDUCE CELL SIZE BY AGGREGATING PIXELS
REPLACE THE CELL (AND VALUE) BASED ON THE CONDITION OF NEIGHBORING CELLS
ASSIGN NEW RASTER VALUES USING RECLASSIFICATION
CALCULATE STATISTICS OF MULTIPLE RASTERS
GET THE FREQUENCY OF WHEN A RASTER IS LESS, EQUAL, OR GREATER THAN ANOTHER RASTER S CELL VALUES
CALCULATE THE AREA OF A ASTER/FEATURE WHEN IT FALLS INTO EACH ZONE OF ANOTHER RASTER/FEATURE
CALCULATE THE GEOMETRY OF A RASTER IN EACH ZONE
DATA PREPROCESSING FOR THE MERAUKE PROJECT Ophelia Wang, Department of Geography and the Environment, University of Texas
DATA REQUIREMENTS 1. All data layers must share the same spatial extent, total number of cells, cell size, and cell ID 2. Within the oil concession zone--- Cell size = 100 m 166,028 cells
GENERATING AN ANALYSIS MASK Mask: a habitat layer derived from classifications of land cover and flooded areas, and maps of geology groups and topographic position index
In ArcGIS: Convert the habitat raster to point shapefile each point has an ID convert the points back to raster using the IDs the raster value of each cell represents cell ID use as mask
LIST OF OTHER LAYERS Production suitability 2-km buffers around each village 500-m buffers around each sacred site or cultural site Rarity Hydrological-wetland connectivity Community-assigned habitat usage scores (six community layers)
PRODUCTION SUITABILITY (5 OR 10 CLASSES) Suitability map on a gradient of 0-255 across the broader Merauke landscape Regrouped to 5 suitability classes for areas within the concession boundary; 5= high, 1=low (Map source: Conservation International)
VILLAGES WITH 2-KM BUFFERS Village point shapefile create a 2-km buffer around each point convert buffers to raster use the cell ID mask raster calculator: con(isnull[buffer], 0, [buffer]) (same process to create sacred + cultural 500-m buffer layer)
SACRED + CULTURAL SITE BUFFERS NOT OVERLAPPING WITH VILLAGE BUFFERS Overlapped area between village buffers and sacred + cultural buffers: [village] & [sac+cul] calulation con([calculation]==1, 0, [sac+cul]) sacred + cultural site buffers not overlapping with village buffers
RARITY AND HYDROLOGICAL CONNECTIVITY LAYERS (MASKED USING SPATIAL ANALYST )
COMMUNITY-ASSIGNED SCORES FOR HABITAT TYPES BASED ON USAGE Four important habitat types to use for ConsNet: Flooded savannas, savannas, dry forest, and open land/grassland Reclassify in ArcGIS: remain the codes for the above four habitats and assign other habitats to 0 (done for six community layers)
COMMUNITY BOUNDARY LAYERS Use the community score layers for habitats con([score]>0, 1, [score]) Six community boundary layers Four scores remained
OTHER POTENTIAL LAYERS Sago (a type of resource use) site buffers not overlapping with village buffers Community boundary Distance between the centroid of each cell to the nearest village, sacred, or cultural site (Convert the cell ID points to raster using the distance as value, each cell value = distance
Estimating soil erosion rate based on soil, slope, hydrology, and land cover A = R * K * LS * C * P A = estimated average soil loss in tons per acre per year R = rainfall-runoff erosivity factor K = soil erodibility factor L = slope length factor S = slope steepness factor C = cover-management factor P = support practice factor
MODEL BUILDER EXAMPLE: SOIL EROSION
FLOW ACCUMULATION LAYER DERIVED FROM FLOW DIRECTION LAYER
MAKING SLOPE LAYER FROM SURFACE ANALYSIS TOOL
The results indicates the areas prone to soil erosion based on the calculations. On the layer erosion, the darker areas (areas of higher values) are most likely to suffer from future soil erosion.