Post on 06-Apr-2018
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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