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NSF DUE-1205110; 0903270
OverviewBuffersOverlays
ClipIntersectionUnionDissolveMerge
Spatial Joins
Module 4.3, Overlays and Buffers
NSF DUE-1205110; 0903270
BuffersCan add a buffer to a point, line, or polygonPay attention to map units when specifying
buffer distance
NSF DUE-1205110; 0903270
What is an overlay?Take two or more layers
Typically with the same extent (they are one on top of another)
Combine the layers in some waySpecific overlay techniques
Create an output layer
Layer 1Layer 2
New Layer
NSF DUE-1205110; 0903270
ProjectionsBefore beginning any overlay type operation,
be sure you have the same coordinate systems throughout the map document
This will avoid crashing the program or inaccurate results
NSF DUE-1205110; 0903270
Overlaying Vector DataCommon vector overlay/geoprocessing
operationsClip (cookie cutter)Intersect – keeps only common features
between two layersUnion – combines all features in two layersDissolve – combine (simplify) features in one
layerMerge – combine two layers into one
Always recalculate areas/perimeters of polygons after one of these operations
NSF DUE-1205110; 0903270
ClipUse one layer as a boundary to clip (cut) out
features from another layer
NSF DUE-1205110; 0903270
More on clipBe sure you have correct layers as the input
layer (the one to be cut) and the clip layer (the one to use as a cutting guide)
Must use polygons as the clip layerCan use selected features or all features as a
clip layer
NSF DUE-1205110; 0903270
IntersectCombines two layers and outputs only the
features common (spatially) to both layers
NSF DUE-1205110; 0903270
More on IntersectBe sure you know which layer is the input
layer and which is the overlay layerThe overlay layer must be polygonsAttributes will come from both layersWill need to re-calculate polygon areas
NSF DUE-1205110; 0903270
More on UnionBe sure you know which is the input and
which is the overlay layerMay use all or selected features as overlayOverlay must be polygonAttributes will come from both layers
NSF DUE-1205110; 0903270
DissolveCombine features in a layer based on one
attributeExample: aggregate counties in US by state
name
NSF DUE-1205110; 0903270
More on DissolveHave to specify common featurePoints, lines, and polygonsNeed to specify how to deal with remaining
attributesFirst or lastSum, min, max, mean
NSF DUE-1205110; 0903270
More on MergeCan have multiple layersMust specify which layer will define attribute
table fields for the outputNeed to be aware of:
Differing attribute tablesPresence of gaps (spatially) in merged layers
NSF DUE-1205110; 0903270
Summary: vector overlayPowerful tools for creating new informationConsider attributesRecalculate area and perimeterFiles with different coordinate systems can
cause problems – convert coordinate systems first
NSF DUE-1205110; 0903270
Spatial JoinSpatial joins match the join layer to a target
layer – creating a new output layer that contains attributes from both layersBased on their proximity Based on inputs from you
To learn more about Spatial Joins, open ArcMap help
Search for “Spatial Joins by Feature type”