1. Intro. To GIS Lecture 6 Spatial Analysis April 8th, 2013

2. Reminders
Please submit your homework
Project?

3. Spatial Features Types of features in GIS
Point  Nest Site; gas stations
Line  Movement Path; River;
Polygon  Home Range; Nest Plot
Note: When we talk about features we mean vector datasets

4. Spatial Features cont. Feature Class
Group of features of the same geometry
Can be filed in different formats
Shapefile

6. 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

7. BASIC SPATIAL ANALYSIS TOOLS IN A GIS
database queries
Selection/selection by location
Spatial joins
basic statistics
Functions (Tools)
Dissolve
Buffering
Near
overlay

8. GIS ANALYSIS TOOLS

9. QUERIES Ask 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)

10. QUERIES Where are the thinnable stands?
Age  30 and Age  Age  30 and Age  40 and MBF  30

11. QUERIES Structured 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

12. QUERIES
Example:
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)

13. QUERIES: Not always the Best
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

14. 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

15. 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.

16. 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

17. Right Click on the Field
Go to “Summarize”
Choose statistic to summarize

18. 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

19. 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

20. Functions (Tools): Types of Analysis
Layer 1
Function 1
Layer 2
Function 2
Layer 3
Function
Layer 2
Layer 1
Layer 3

21. Dissolve Tool
Similar to the merge function in Editor toolbar

22. Dissolve Tool Input Features Output Feature Class
Dissolve field(s) (optional)
Statistics (optional)
Create multipart features (optional)

23. Buffering
Buffering creates a polygon using a specified distance from a point, line, or other polygon

24. Buffer Tool Input Features Output Feature Class Distance Side/End type
Linear unit (pick units)
Field (attribute table)
Side/End type
Dissolve Type

25. Buffer application 500 ft. buffer applied to houses
Buffer overlaps transfer station

26. Multiple-Ring Buffer Creates buffers for many distances at once
Dissolve option makes them non-overlapping

27. Near Tool
Calculates distance from input features to nearest feature in other layer(s)

28. 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)

29. Near Application

30. Overlay
Intersect
Identity
Symmetrical Diff.
Union
Clipping/Erasing

31. Intersect (AND Operator)
Polygons split at feature boundaries of both datasets
Only overlapping areas are kept
Attribute tables are updated in output

32. Identity Similar to intersect but input features are not clipped
Features split along identity polygon edges
Attribute tables are combined in output

33. Symmetrical Difference (XOR Operator)
Simply differencing the two layers (overlapping areas are ignored)

34. Union (OR Operator)
Like Intersect but both input and union features are retained
Output features have attributes from both input and union layers

35. Clipping Using one layer like a cookie cutter for another
Any vector can be used as input
Clip feature must be a polygon

36. Erasing The opposite of clipping
Erase feature used to remove a portion of the input data (point, line, or polygon)

37. Intersect / Identity / Union
Which function is which?

38. Summary

39. GIS Technology: Relationship between Land use and Crop Productivity
Soil Type
Overlaid with
Crops Production
(ton/ha)
Overlay Analysis
Overlay Result
GIS Technology: Relationship between Land use and Crop Productivity

40. 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

41. 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