Vector Analysis Ming-Chun Lee

Spatial Analysis What is Spatial Analysis? Spatial analysis is a set of methods whose results change when the locations of the objects being analyzed change. Turning raw data into useful information Reveal things that might otherwise be invisible What is Spatial Analysis? Spatial analysis is a set of methods whose results change when the locations of the objects being analyzed change. Emphasis spatial analysis is about spatial data Location-sensitive Select by location, location changes definitely change the selection result Select by attribute, location changes, the distribution of the selection result may also change.. For example: select bus route passing through downtown, but some of bus routes may be moved, then your selection result chnage Turning raw data into useful information Reveal things that might otherwise be invisible, or say incomprehensible

Spatial Analysis Turning raw data into useful information Extracting or creating new information about a set of geographic features and examining the relationships between them. The set of geographic features used in spatial analysis could pertain to data within only one layer or within two or more layers depending upon the users needs. Turning raw data into useful information Extracting or creating new information about a set of geographic features and examining the relationships between them. The set of geographic features used in spatial analysis could pertain to data within only one layer or within 2 or more layers depending upon the users needs. Last week, we looked at how you can select data, by location or by attributes, how you can re-classify a dataset, those are all applied to a single dataset. today, we will look at some other tools allow you to do spatial analysis on multiple layers..

Spatial Analysis Methods range from simple to sophisticated Usually involves manipulations or calculation of coordinates or attribute variables with a various operators (tools), such as: Selection Measuring Reclassification Dissolving Overlay Buffering Methods range from simple to sophisticated Usually involves manipulations or calculation of coordinates or attribute variables with a various operators (tools), such as: Selection Measuring Reclassification Dissolving Overlay Buffering

Selection Can be invoked on spatial and attribute components Selection by Attributes Selection by Locations Involves selective search No new objects created example: lots owned by foreigners (attribute) example: lots along the substation buffer (location) Can be invoked on spatial and attribute components Selection by Attributes Selection by Locations Involves selective search - data query No new objects created example: lots owned by foreigners (attribute) example: lots along the substation buffer (location)

Measurements Getting numerical values that describe aspect of data Length Area Many tasks require measurement from maps measurement of distance between two points measurement of area, e.g. the area of a parcel of land Getting numerical values that describe aspect of data Length Area Many tasks require measurement from maps measurement of distance between two points measurement of area, e.g. the area of a parcel of land

Reclassification Classification - identify a set of characteristics to group together objects. In a vector system, classification involves addition of objects characteristics. (join a table) In a raster system, classification involves converting or coding cell values. Classification examples: Land parcels for housing are classed into single-family and multi-family Classification provides new patterns/relationships Classification - identify a set of characteristics to group together objects. In a vector system, classification involves addition of objects characteristics. (join a table), base on additional information In a raster system, classification involves converting or coding cell values. Classification examples: Land parcels for housing are classed into single-family and multi-family Classification provides new patterns/relationships Reclassification does not create new dataset, just provide new information

ORIGINAL CLASSIFICATION GENERALIZED CLASSIFICATION Reclassification URBAN RESIDENTIAL INDUSTRIAL RURAL FOREST AGRICULTURE ORIGINAL CLASSIFICATION GENERALIZED CLASSIFICATION The way we look at the dataset different

Overlay Analysis Combination of different data layers Both spatial and attribute data is combined Produces new layers Involves two or more data layers You can only overlay or analyze two themes But you can combine two into one and then deal with the third one and so one; input theme can be point/line/polygon, but overlay needs to be a polygon All themes need to be spatially registered Need to have same coordinate system Combination of different data layers Both spatial and attribute data is combined Produces new layers Involves two or more data layers You can only overlay or analyze two themes But you can combine two into one and then deal with the third one and so one; input theme can be point/line/polygon, but overlay needs to be a polygon All themes need to be spatially registered Need to have same coordinate system

Overlay Analysis Until the arrival of GIS Map overlay analysis was performed manually Superimposing transparent map layers on a light table to identify sites simultaneously meeting a number of criteria Overlay operations can be performed in vector/ raster-based GIS Overlay operation is a key analytical capability of a GIS New data can be created by combining two or more input data Overlay is a common means doing spatial analysis, even before GIS was invented… Until the arrival of GIS Map overlay analysis was performed manually Superimposing transparent map layers on a light table to identify sites simultaneously meeting a number of criteria Overlay operations can be performed in vector/ raster-based GIS Overlay operation is a key analytical capability of a GIS New data can be created by combining two or more input data

Overlay Analysis

Overlay Analysis

Vector vs. Raster Vector Overlay Raster Overlay URBDP 498w - Introduction to GIS in Planning Lecture 8

Vector Overlay Based on geometry and topology Vector overlay operation results in a more complex output layer More polygons / intersections / line segments than input layers Calculates new topology and associated attributes More time-consuming, complex and computationally expensive, in comparison with raster-based overlay operations Based on geometry and topology Vector overlay operation results in a more complex output layer More polygons / intersections / line segments than input layers Calculates new topology and associated attributes More time-consuming, complex and computationally expensive, in comparison with raster-based overlay operations

Raster Overlay Cell by cell process which results in the combination of the two input layers known as map algebra operations include boolean, multiply, and algebra Cell by cell process which results in the combination of the two input layers known as map algebra operations include boolean, multiply, and algebra

Three Types of Vector Overlay Point-in-Polygon Points are assigned attribute of polygon E.g. wildlife (point) and assoc. with vegetation (poly) Line-in-polygon Original lines are dissected by polygon boundary Lines will have attribute of lines and polygons E.g. roads and soil types along roads Polygon-on-polygon Each new polygon will have attribute from both E.g. elevation and vegetation or elevation and rainfall Point-in-Polygon Points are assigned attribute of polygon E.g. wildlife (point) and assoc. with vegetation (poly) Line-in-polygon Original lines are dissected by polygon boundary Lines will have attribute of lines and polygons E.g. roads and soil types along roads Polygon-on-polygon Each new polygon will have attribute from both E.g. elevation and vegetation or elevation and rainfall

Boolean Logic Determines the binary properties of features True-false, yes-no, or presence-absence Rather than using numbers and magnitudes of features Reduces measures to some binary condition Simplifies the results of overlay operations Determines the binary properties of features True-false, yes-no, or presence-absence Rather than using numbers and magnitudes of features Reduces measures to some binary condition Simplifies the results of overlay operations

Boolean Logic A NOT B A A&B B B NOT A Union (A or B) Intersection (A & B)

Boolean Logic

Buffering Common GIS operation A type of proximity analysis where a buffer zone is created to perform a search Buffer: encloses point, line, or polygon at specified distance. Search: specify a distance from a point (radius), line (corridor), area (area) New spatial objects created Common GIS operation A type of proximity analysis where a buffer zone is created to perform a search Buffer: encloses point, line, or polygon at specified distance. Search: specify a distance from a point (radius), line (corridor), area (area) New spatial objects created

Buffer Generation Buffering a Point Buffering a Line Buffering an Area All area within one mile of a city Buffering a Line All areas within 100 meters of a road Buffering an Area All areas within 500 meters of a wetlands area. Buffering a Point All area within one mile of a city Buffering a Line All areas within 100 meters of a road Buffering an Area All areas within 500 meters of a wetlands area.

Buffer Generation Buffering possible with raster or vector data models

Vector Analysis Dissolve Overlays for Merging Diverse Layers ArcToolbox Dissolve Overlays for Merging Diverse Layers UNION INTERSECT IDENTITY Overlays for Trimming Diverse Layer Extents CLIP ERASE Combining Similar Layers with Different Extents MERGE UPDATE Creating Proximity- Based Polygon Layers: BUFFER Dissolve ArcMap Dissolve Regions ArcToolbox Dissolve Overlays for Merging Diverse Layers UNION INTERSECT IDENTITY Overlays for Trimming Diverse Layer Extents CLIP ERASE Combining Similar Layers with Different Extents MERGE UPDATE Creating Proximity-Based Polygon Layers: BUFFER

DISSOLVE ArcMap Merges Non- Adjacent Polygons GeoProcessing Wizard Operates on Shapefiles, Coverages Merges Non- Adjacent Polygons ID Color A Purple B C Blue D Green E A D C B E ID Color A Purple C Blue D Green D A C ArcMap GeoProcessing Wizard Operates on Shapefiles, Coverages Merges Non-Adjacent Polygons D

UNION Combine Only the Common Extents of Both Layers Preserve All Attributes Combine Only the Common Extents of Both Layers Preserve All Attributes URBDP 498w - Introduction to GIS in Planning Lecture 8

INTERSECT Combine Full Extents of Both Layers Preserve All Attributes

IDENTITY Combine Only the Extents of the Original Layer Preserve All Attributes Combine Only the Extents of the Original Layer Preserve All Attributes URBDP 498w - Introduction to GIS in Planning Lecture 8

CLIP Trim the Original Layer to Only the Extents of the Clip Layer Preserve Only the Original Layer’s Attributes Trim the Original Layer to Only the Extents of the Clip Layer Preserve Only the Original Layer’s Attributes URBDP 498w - Introduction to GIS in Planning Lecture 8

ERASE Trim the Original Layer to Exclude the Extents of the Clip Layer Preserve Only the Original Layer’s Attributes Trim the Original Layer to Exclude the Extents of the Clip Layer Preserve Only the Original Layer’s Attributes URBDP 498w - Introduction to GIS in Planning Lecture 8

MERGE/APPEND Add Non-Overlapping Extents of Multiple Layers Preserve Consistent Attributes Add Non-Overlapping Extents of Multiple Layers Preserve Consistent Attributes

UPDATE Add Overlapping Extents of Multiple Layers Preserve Consistent Attributes Within Shared Extents, Give Preference to Newer Layer Add Overlapping Extents of Multiple Layers Preserve Consistent Attributes Within Shared Extents, Give Preference to Newer Layer

Summary of Overlay Operations Original Extents Original Attributes New Extents New Attributes UNION Overlap Different Total All INTERSECT Shared Only IDENTITY Layer A CLIP Layer B ERASE Layer A–B MERGE No Overlap Same UPDATE All* * Giving Preference to Layer B when A & B Conflict

BUFFER Create a Polygon Layer with Boundaries at a Specified Distance from Another Layer Fixed Distance Variable Distance Based on an Attribute Series of Buffers Create a Polygon Layer with Boundaries at a Specified Distance from Another Layer You can make a buffer surround a point, a line, or another polygon.. Three different ways you can specify the distance for a buffer: Fixed Distance Variable Distance Based on an Attribute Series of Buffers

BUFFER Fixed Distance Examples: Walking Distance to Bus Stops Areas of Street Light Illumination

BUFFER Examples: Noise Levels By Street Type Variable Distance Based on an Attribute Examples: Noise Levels By Street Type

BUFFER Examples: Walking Distance to Bus Stops Series of Buffers Examples: Walking Distance to Bus Stops Areas of Street Light Illumination

Tools for Spatial Analysis All of these tools are found in ArcToolbox in ArcMap

Example of Vector-Based Analysis Find suitable sites for a new arboretum Site Criteria: Within county limit Deep, Fertile, Loamy Soils Forested Land More than 1 km from major rivers Between 2 and 4 kms from major roads

County Boundary

Major Roads Clipped to County

Major Rivers Clipped to County

Buffer Rings on Roads 2-4 km

Buffer of Roads >2km <4km

Land Use

Forest Land Cover

Clip Forest LC to Roads

County Soils

Deep, Fertile, Loamy Soils

Clip Soils to Roads

Intersect Soils and LC

Select SOIL/LC within 1km of Rivers

Switch Selection

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