intro. to gis lecture 6 spatial analysis april 8 th , 2013
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Intro. To GIS Lecture 6 Spatial Analysis April 8 th , 2013. Reminders. Please submit your homework Project?. Spatial Features. Types of features in GIS Point Nest Site; gas stations Line Movement Path; River ; Polygon Home Range; Nest Plot. - PowerPoint PPT PresentationTRANSCRIPT
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Intro. To GISLecture 6
Spatial AnalysisApril 8th, 2013
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Reminders
• Please submit your homework
• Project?
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Spatial FeaturesTypes of features in GIS
1) Point Nest Site; gas stations
2) Line Movement Path; River;
3) Polygon Home Range; Nest Plot
Note: When we talk about features we mean vector datasets
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Spatial Features cont.
• Feature Class– Group of features of the same geometry– Can be filed in different formats
Shapefile
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Spatial Analysis
• The application of operations to coordinate and related attribute data
• Maps are great, but this is the real power of GIS
• Spatial analysis is used to explore or solve a problem using a variety of geoprocessing tools
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BASIC SPATIAL ANALYSIS TOOLS IN A GIS
database queries Selection/selection by location
Spatial joins basic statistics Functions (Tools)
Dissolve Buffering Near overlay
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GIS ANALYSIS TOOLS
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QUERIESAsk questions about GIS databases: Where are the older stands? Which roads are paved? Which trails are authorized? Which water sources are within a certain distance of a
road?
Note that the queries do not inherently result in a new layer… They usually only highlight features (which could be exported to a new layer afterwards)
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QUERIESWhere are the thinnable stands?
Age 30 and Age 40 Age 30 and Age 40 and MBF 30
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QUERIESStructured Query Language (SQL) uses standard operators
e.g. = > < + - * “and” “or” “not”
standard order of operations add/subtract before multiply/divide use parentheses to “isolate” terms
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QUERIESExample: select stands greater than 30 acres with grass
understories and a mean quadratic diameter less than 20 inches.
query for above:
(area > 30) and (understory = “grass”) and (QMD < 20)
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QUERIES: Not always the Best
#Y#Y#Y
#Y #Y
Which water sources are within a certain distance of a road?
we need more information.
perhaps a new database layer.
“buffering” may help answer this question
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Spatial Joins• Joins attributes from one feature class
to another based on a spatial relationship (INTERSECT, CONTAINS, WITHIN, CLOSEST)
– points in polygon (identifies polygon in which point is located)
– polygon in polygon (identifies polygon in which polygon is located)
– lines in polygon (identifies polygons crossed by line)
– points on lines (calculate distance to nearest line)
– points on points (calculate distance to “nearest neighbor” point)
operate on tables and normally creates a new table with additional variables, but does not modify spatial features themselves
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Query Vs. Spatial Join• Selection: simply selects (“highlights”) entire spatial features in the
target layer, but doesn’t modify these features
– Selection only– Only Selected features (a subset of all features) are “output”– No new output file saved unless you use Export/data
• joins: operate on tables and normally creates a new table with additional fields or variables (columns), but again does not modify actual spatial features (rows)
– adds attributes (columns) to the layer’s table from another layer’s table– All features are “output”– No features modified– No new output file saved unless you use Export/data
Note: Different approaches can be used, in some cases, to produce same results.
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BASIC STATISTICS statistics can help determine meaning
within the data simple, sum, count, mean, maximum,
range, variance and standard deviation calculates statistics for a combination of
fields, for example: by combining the ‘State’ name field &
‘Population’ fields, we can calculate the average state population
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• Right Click on the Field• Go to “Summarize”
Choose statistic to summarize
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BASIC STATISTICS: Calculating Fields
• New values can be calculated based on other attribute values
• Simple algebra and more advanced math operations
• Text functions for picking part of a string or modifying case
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BASIC STATISTICS: Calculate Geometry
• Length, Area, or X,Y coordinates
• Choose coordinate system of source or data frame
• Pick units of measurement
• Make sure field has units in the name
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Functions (Tools): Types of Analysis
Layer 1
Function 1 Layer 2
Function 2 Layer 3
Function
Layer 2
Layer 1Layer
3
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Dissolve Tool– Similar to the merge function in Editor
toolbar
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Dissolve Tool
• Input Features• Output Feature Class• Dissolve field(s)
(optional)• Statistics (optional)
• Create multipart features (optional)
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Buffering• Buffering creates a polygon using a
specified distance from a point, line, or other polygon
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Buffer Tool
• Input Features• Output Feature
Class• Distance
– Linear unit (pick units)
– Field (attribute table)• Side/End type• Dissolve Type
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Buffer application• 500 ft.
buffer applied to houses
• Buffer overlaps transfer station
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Multiple-Ring Buffer• Creates buffers for many distances at
once• Dissolve option makes them non-
overlapping
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Near Tool
• Calculates distance from input features to nearest feature in other layer(s)
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Near Tool• Output has field with ID
and distance of feature
• Multiple near layers can be calculated at once
• Options to include:– Location (X,Y)– Angle (degrees)
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Near Application
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Overlay
• Intersect
• Identity
• Symmetrical Diff.
• Union
• Clipping/Erasing
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Intersect (AND Operator)
• Polygons split at feature boundaries of both datasets
• Only overlapping areas are kept
• Attribute tables are updated in output
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Identity• Similar to
intersect but input features are not clipped
• Features split along identity polygon edges
• Attribute tables are combined in output
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Symmetrical Difference (XOR Operator)
• Simply differencing the two layers (overlapping areas are ignored)
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Union (OR Operator)• Like Intersect
but both input and union features are retained
• Output features have attributes from both input and union layers
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Clipping• Using one layer
like a cookie cutter for another
• Any vector can be used as input
• Clip feature must be a polygon
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Erasing
• The opposite of clipping– Erase feature used to remove a portion of
the input data (point, line, or polygon)
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Intersect / Identity / UnionWhich function is which?
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Summary
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Soil Type
Overlaid with
Crops Production(ton/ha)
Overlay Result
GIS Technology: Relationship between Land use and Crop Productivity
Overlay Analysis
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Spatial Analysis Tips
• Using these tools in conjunction with each other can produce some useful data– Clip a polygon using a buffer– Calculate new fields to determine percentages
• Name your output files so you will remember the inputs and the tool you used– i.e. (LandUse_Buffer_Intersect.shp)
• When in doubt, check the help documentation
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Homework & Lab
• HW 7: Ch. 6 p. 149 – 165, answer Q’s 1, 3, 4, 12
• Lab this week: Spatial (vector-raster) Analysis– The instructions will be given (Do NOT
bring your lab book on Wed)• Next lecture would be on April 17th