1. Basic Spatial Analysis
Spatial Data Analysis: Dealing with GIS functions of storing and querying spatial data
May 30, 2013
Institute of Space Technology, Karachi

2. Spatial Analysis
Involves applications of operations to coordinates and related attribute data
Spatial functions or operations: Manipulation or calculation of coordinates or attribute variables.

3. Chapter 9 of your text book.

4. Input Layer  Spatial Operation Output Layer
Spatial Data Analysis
Input Layer  Spatial Operation Output Layer
Spatial analyses are applied to solve problems related to geographic decisions
Examples:
Identify high crime areas
Generate a list of road segments that need repaving
Select a best location for a new business
100s of spatial operations or functions. E.g.: high crime area, spread of disease etc.
A chain of spatial operation (sequentially) – out of each serving as input to the next operation
Data from 1 or 2 layers to create output

5. Sequence of Spatial Operations
Single Spatial Operations
Sequence of Spatial Operations
Spatial operations can be applied sequentially to solve a problem.
Output of each spatial operation serving as input of the next.

6. Challenge!!!!
Selecting appropriate spatial operations and applying them in the appropriate order

7. Spatial Data Analysis Non Spatial Queries (standard Database queries)
Application of operations to coordinates and
related attribute data
Non Spatial Queries (standard Database queries)
How long is River Indus?
Population of Pakistan?
etc.
Spatial Queries
Neighboring countries of Pakistan?
List of provinces through which Indus river flows?
Spatial operations/function to calculate
These are standard Database queries that request to retrieve the value of some attribute.
Spatial operations that applied to both coordinate and associated attribute data?

8. Spatial Data Analysis
Since attribute data is related to spatial objects therefore we can not separate operations on attribute data from operations on coordinate portion of spatial data

9. Spatial Operations
Applied to one or more input layers to produce one or more output data layers
One to One
Conversion of raster data into vector
One input – Many outputs
Slope and aspect produced from raster elevation model
Many inputs – one output
To calculate data averages from different layers
~takes input data, performs analysis on it, and produces output information (may be a layer or non spatial-mean cell value of a raster data layer)
Slope (how steep each cell is) and aspect (direction of slope): Terrain analysis function
Many input: mean temperature over last ten years,

10. Spatial Operations
Spatial function or operations are basic components of spatial data analysis.

11. Spatial Operations Depends on type of data model used
Specific operations available in the GIS software
In many instances it’s more efficient to convert data between data models and apply the desired operations and convert results back to the original data model

12. Spatial Operations Outputs
Non Spatial outputs
Spatial operation produces scalar value, a list, or a table with no explicit geometric data attached
Spatial
New data layer is produced
Non-spatial: in raster data set mean cell value
Aspatial: list of all land cover types extracted from a data layer

13. Spatial Scope Local Operations Neighborhood Operations
Spatial operations may be
characterized by their spatial scope
Local Operations
Neighborhood Operations
Global Operations
Scope: to reflect the extent of the source area used to determine the value at a given output location.
Local Operations: data at one input location. Attributes of adjacent locations are not used
Neighborhood Operations: use both an input location + nearby location to determine output value. Value at an output location is influenced by more than just the value of data found at the corresponding input location
Global Operations: uses data values from the entire input layer to determine each output value

14. Spatial Data Analysis Selection Reclassification Dissolving Buffering
Overlay
Set of available spatial operation depends on the data model and type of spatial data used as input.
Data model conversion may also be a choice for ease in spatial operation application.
selection operation from relational algebra
Reclassification: Raster operation???

15. Selection Features are identified based on given criteria
Example: in a political map of European countries, select all names and population of countries with more than 50M inhabitants
Above is an example of set algebra
>, <, =, & <>
Used either alone or in combination
On-screen or interactive query
Selection by attribute
Selection by location
Selection by graphics
ArcToolbox: Analysis Tools-Extract-select
The set algebra operations < & > not applied on nominal data because there is no implied order in nominal data.

16. Selection
Thematic map of countries of western Europe (and their population); selection of countries with more than 50M people

17. Selection: Set Algebra
Set algebra uses operations > < = <>
And < can not be applied to nominal data. There is no implied order in nominal data. Green is not greater than Red.
All applied to ordinal and ratio/interval data

18. Selection Boolean Algebra Conditions: AND, OR, NOT
Combines set algebra and create compound spatial selection
Boolean expression is valuated by assigning an outcome 1, 0 or True, False

19. Expression In Boolean Algebra

20. Selection by Location Adjacency Containment
Adjacency and Containment are 2 commonly used selection operations.
States adjacent to Missouri
Adjacency: Shared line/node required.
Containment: States containing a portion of Mississippi River or its tributaries are selected

21. Reclassification
Classification of spatial objects based on spatial or non spatial data
Example: classification of Polygons based on size
Examples of Reclassification
Equal Interval
Equal Area
etc.

22. Dissolve Combines or dissolve similar features within a data layer
Adjacent polygons with identical values are merged into a single polygon
Often used after reclassification

23. Proximity
Modifies existing feature or creates new features that depend on distance
Available water represented by Points and distance function applied to these points to create raster data layer containing the distance to nearest water feature.
What neighborhoods are far from utility stores.
Which homes will be affected by an increase in freeway noise. .

24. Proximity: Distance Calculations
Distance values are calculated using Pythagorean formula
Calculated from cell center to cell center (when applied to raster data)

25. Represents specific distance around a feature
Buffers
Commonly used proximity function
Represents specific distance around a feature
May be determined for point, line, or area features
Also for both types of data models
Most common spatial analysis tool.
Less than or equal to a specified distance from one or more features.

26. Overlay Overlapping different themes (multiple layer operation)
Areas where features in different layers overlap
Both spatial and attribute data is combined
Clip, Intersect and union are special cases of overlay
A new data layer is created

27. Vector Overlay Clip Intersect Union
Only the areas that overlap are contained
Cookie cutter approach
Intersect
Combines data from both layers but only for a given region where both layers contain data
Union
Both overlapping and non-overlapping areas are contained
Order of intersection is important

28. Overlay - Examples
Overlay output typically takes the dimension of the lowest order input.

30. Raster Overlay Cell by cell combination of 2 or more data layers
Typically applied to nominal or ordinal data

31. Geoprocessing in ArcGIS
Set of software functions used to manipulate and transform spatial data (single layers or multiple sets of layers), to create new information
Map Overlay functions: combining layers to create single output
Extraction
Intersection
Dissolve
Buffer
Append and Merge

32. Extraction Clip: cookie cutter function Erase: Opposite of clip
Layers to be clipped: point, line, polygon
Clipping layer:
When the Input Features are polygons, the Clip Features must also be polygons
When the Input Features are lines, the Clip Features can be lines or polygons.
When the Input Features are points, the Clip Features can be points, lines, or polygons.
Erase: Opposite of clip
Layer attributes not combined
Clip: Features inside the clip boundary will be preserved, all those outside are removed. A feature is used as a cookie cutter to cut the extent of another feature to the same extent as the cookie cutter feature.
Erase: all information outside of the operational polygon are preserved, and the interior features are erased

33. ArcGIS Desktop –Resource Center

34. ArcGIS Desktop -Resource Center

35. Intersection & Union Intersect Union
Merges attributes between layers, points-lines-polygons
Union
Combines two polygon layers, keeping all areas and merging attributes
Layer Attributes combined
Integrate two spatial data sets while preserving only those features falling within the spatial extent common to both themes

36. Intersection & Union

37. Dissolve Combines and dissolves similar features within a data layer
Aggregates features based on the same attribute value specified by the user

38. Buffers
Creates region at specific distance from one or more features

39. Buffers Undissolved Buffer Dissolved Buffers Separate Polygons
Merged Polygons

40. Append and Merge Combine 2 layers into 1
Merge “edges” of adjoining layers with identically matching polygons and attributes
Append data while maintaining the attributes contained in the selected layer
Combines two layers of the same feature-type (points, lines, or polygons).

41. ARcGIS Tool for Geoprocessing
To be covered in Lab

42. a. Clip tool
ArcTool Box- Analysis Tools – Extract - Clip
b. Erase tool
ArcTool Box – Analysis Tools – Overlay - Erase
c. Intersect tool
ArcTool Box – Analysis Tools – Overlay – Intersect
d. Union tool
ArcTool Box - Analysis Tools – Overlay - Union
e. Dissolve tool
Arc Tool Box – Data Management Tools – Generalization - Dissolve
f. Buffer tool
ArcTool Box - Analysis Tools – Proximity - Buffer
g. Append tool
Arc Tool Box – Data Management Tools-General – Append
h. Merge tool
Arc Tool Box – Data Management Tools- General – Merge

43. Using Model Builder
Models are built to automate geoprocessing workflow

44. References webhelp.esri.com/.../spatial_operations.htm
_ArcGIS.pdf
NCRG Training Courses, “Introduction to GIS” Prepared by Training, R&D Division
GIS Fundamental by Paul Bolstad

45. Union Query Union operation from relational algebra
Applied ONLY to thematic maps with same attribute schema
Example: union of the map containing European countries with more than 10M inhabitants and the map containing European countries with less than 10M inhabitants. The two maps both have schema (name, population)

46. Union Query
Thematic map of countries (and population) of western Europe with more than 10M inhabitants
Thematic map of countries (and population) of western Europe with less than 10M inhabitants