Vector Based Analysis

8/3/2019 Vector Based Analysis

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Point in polygon

Line in polygon

Polygon in polygon Overlay operations


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Until the arrival of GIS, map overlay analysisis performed manually by superimposingtransparent overlays of map layers on a

light table to identify sites simultaneouslymeeting a number of criteria.

The ability to integrate variety of datasources using overlay operation is a key

analytical capability of a GIS. A new data layer can be created by

combining two or more input data layersthrough overlay operations.


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A spatial operation in which one pointcoverage is overlaid with a polygon

coverage to determine which point falls

within the polygon boundaries.

After overlay operations, points assume the

attributes of the polygon within which they

fall.

We can formulate a hypothesis using theanalysis in crime occurrence and

neighborhood demographics, special

species of birds and vegetation.


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Spatial operations in which arcs in onecoverage are overlaid with polygon ofanother coverage to determine whichareas of arcs or portion of arcs are

contained within the polygons. It basically involves evaluating which line

segments intersect arcs of each polygonand locating intersecting node points.

After the operation arcs are assigned theattributes of polygon attributes ofcorresponding polygons within which theyfall.


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A hypothesis can be formulated about the

spatial relationships between the

occurrence of arcs and attributes of

polygon, for example, transportation routes

and urban expansion zones.


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A process that merges spatially coincidentpolygons from two coverages and theirattributes to create a third coverage thatcontains new polygons and describe newrelationships.

After overlay, the resultant polygon entitiesare known as the least commongeographical unit(LCGU).

The topology of the new polygon coveragemust be computed and multiple attributesfrom the input coverage should beassigned to LCGU.


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One problem with the vector overlay is the

generation of sliver polygons which arise

from inconsistencies and inaccuracies in

the digitized data.

Polygon overlay is often used for site

selection or suitability analysis.


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Union

Identity

Intersect Update

Clip

Split Erase


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Overlay analysis manipulates spatial data

organized in different layers to create

combined spatial features according to the

logical operators.

Commonly used logical operators are :

AND -Common area/Intersection/Clipping

OR - Union or Addition

NOT Inverter

XOR - Minus


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UNION(Boolean OR Logical overlay)

Overlay polygons and keep all features

from both coverages.


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IDENTITY:

Overlay points, lines or polygons on

polygons and keep all input coveragefeatures plus those portions of the polygon

coverage that overlap the input coverage.


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INTERSECT (Boolean AND Logical Overlay)

Overlay points, lines or polygons on polygons

but keeps only those portions of the features

that fall within the spatial extent common to

both input and overlay coverages.


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UPDATE:

Merge new features using a cut and

paste operation to update coverage.


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CLIP:

Extract a subset of features by cutting out a

piece of a coverage.


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SPLIT:

Split a coverage into a number of smaller

coverages.


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ERASE:

Remove part of the inside of a coverage.


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THANK YOU

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Vector Based Analysis