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

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

Chapter 9 of your text book.

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

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.

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

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?

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

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,

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

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

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

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

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???

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.

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

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

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

Expression In Boolean Algebra

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

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.

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

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. .

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

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.

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

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

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

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

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

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

ArcGIS Desktop –Resource Center

ArcGIS Desktop -Resource Center

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

Intersection & Union

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

Buffers Creates region at specific distance from one or more features

Buffers Undissolved Buffer Dissolved Buffers Separate Polygons Merged Polygons

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).

ARcGIS Tool for Geoprocessing To be covered in Lab

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

Using Model Builder Models are built to automate geoprocessing workflow

References webhelp.esri.com/.../spatial_operations.htm http://www.wou.edu/las/physci/taylor/es341/geoprocessing _ArcGIS.pdf www.ianko.com/.../images2/buffer_dissolve.jpg NCRG Training Courses, “Introduction to GIS” Prepared by Training, R&D Division GIS Fundamental by Paul Bolstad

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)

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