arcview
DESCRIPTION
ArcView. Overview. What is arc view What is a shape file. ArcView. AI 8. AE 8. Needed a GUI. AV 8. AV 2. AV 3.x. AV is part of a Family. }. ArcInfo7. ArcGIS. PCArcInfo. ?. AV 1. Shape Files. Shape Files. Topology. - PowerPoint PPT PresentationTRANSCRIPT
esf Laboratory for Applied GIS
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AV is part of a Family
AV 1AV 1
PCArcInfoPCArcInfo
ArcInfo7ArcInfo7ArcGISArcGIS
AV 2AV 2 AV 3.xAV 3.x
Needed a GUI
?
AV 8AV 8
AE 8AE 8
AI 8AI 8
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Topology
• “A mathematical procedure for explicitly defining spatial relationships
• In a COVERAGE topology among polys is explicitly stored in the AAT by – storing adjacent poly Ids in LPoly and RPoly
fields in the database. – By storing in the arc-node table the lines
“adjacent” to one another at nodes
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Topology in Shape Files
• Shape files are non-topological – it does not explicitly store topological relationships
• SF are more like drawings
• However, unlike other simple graphic drawing features they– Store polys as one or more ring structures– A ring is a closed non-self intersecting loop
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Why Topology Anyway?
• One reason was to provide a rigorous, automatic way to clean up digitizing errors
• BUILDing topology forces the identification of errors
• Shape files in AV are created and edited in a feature centric way so that slivers, dangles, missing labels, etc. are never created.
• Digitizing in AV is thus a very different experience and one that we are not going to investigate – except if you do it on your own!
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Rings
12
3
4 5
6
7
89
10
1112
131415
1617
•Walking the ring in clockwise order results in the “inside” poly is always on the right.
In A/V this feature could be 2 polys with two records or 1 poly with 2 parts. Some cmds in A/V can
generate this kind of feature!
Arc 1 Arc 2 Arc 3 Arc 4
Tax parcel 12382
Road right of way
•In the structure a poly can have more than one part!
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Why a different structure?
• Primary advantage of SFs is that the simple data structure allows faster drawing
• A disadvantage is that SFs can be larger than Coverages because shared vertices are not stored twice
• But SFs are not usually 2x the size of a coverage• One reason is that the attribute table of a theme is
a good portion of the size of the file whether it be shape or cover
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Finding adjacent features• Another misunderstanding – AV can find adjacent
polys even though it does not have explicit topology!
selectedSelect by Theme,
Intersect
esf Laboratory for Applied GIS
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Finding adjacent features• Another misunderstanding – AV can find adjacent
polys even though it does not have explicit topology!
selectedSelect by Theme,
Intersect Even
poly
s joi
ned
only
at a
node
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ArcView Terminology
• The Project is the basic AV document. Projects have the extension .apr
• A project holds– Views – the basic window on the graphic
world
– Tables – the attribute data
– Charts – Graphic results of analysis
– Layouts – Map-like graphics
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Views• Views contain the graphic data. A view is made up of:
– A table of Contents (TOC)
– One or more themes of graphic data
– Each theme has a Table “Attributes of xxxxx”
TOC Empty ViewThemes
Active Theme
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Table
• Can be the “attributes of xxxx” or any other data in a database.