different kinds of data example of elevation topographic dem (digital elevation model)
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Different kinds of data
Example of Elevation
TopographicDEM (Digital Elevation Model)
How can elevation be represented in a GIS?
GIS Data Specifics
Getting into the guts of GIS data structure …
Basic structure of Vector and Raster:
PointsLinesPolygons
Attributes
AttributesGrid cells
Remember the idea of a Data Model:
Keep the concept ofdata compression andmachine code in mind…
The Roles of Raster v. Vector Data
CHARACTERISTIC RASTER VECTOR Data structure
Usually simple Usually complex
Storage requirements Large for most data sets without compression
Small for most data sets
Coordinate conversion May be slow due to data volumes, and may require resampling
Simple
Analysis Easy for continuous data, simple for many layer combinations
Preferred for network analyses, many other spatial operations more complex
Positional precision Floor set by cell size Limited only by quality of positional measurements
Accessibility Easy to modify or program, due to simple data structure
Often complex
Display and output Good for images, but discrete features may show “stairstep” edges
Map-like, with continuous curves, poor for images
Going Back to Elevation…
Cartography
Precision (?)of isolines
Calculations
Triangular IrregularNetwork
Data compression
Converting from vector to raster
Converting from raster to vector
Editing!
Yes, you can change data, but do it very VERY carefully!
• Vector data editing• Geoprocessing• Hand digitizing• Attribute table
• Raster adjustments• Calculations• Classification• Deletion of classes• Resampling
Always work in a disposable data copy and save Save SAVE!
Hand digitizing
For example:Creating vector feature classes
based off aerial imagery
Snapping
What this looks like in ArcMap:
Warning:Opening an editingsession in ArcMapchanges how your.mxd functions!
Feature being editedappears with greenbox vertices:
Topology
Topology: The study of geometric properties that do not change as the forms are bent, stretched or undergo similar transformations
Issues with editing – topology rule fixes
Slivers!
Vector feature topology and tables
These tables allowfor fast indexingand searching!
Network example for vector data:NHD (National Hydrography Dataset)
Nodes
Stream Order
Modeling Flow
Direct editing of raster data is limited…
The “Delete Selected”button is what youcan use to edit in araster table
… instead, change rasters with processing!
More Raster Processing
Resampling
Classification
Raster Compression Examples
Run-length coding
Quad-tree compression
Working with vector data attribute tables
Edit attributes directlyHand editing in vector data attribute tables is possible
Joins and Relates – a powerful technique! (Excel is useful here)
Join Types:
One to One
One to Many
Managing Data
DBMS:Database Management SystemControl points for editing
Potential conflicts
Our shapefilesNot centralized
Shapefiles <> File Geodatabase
spatial index format (.sbx)attribute format (.dbf)projection format (.prj)spatial index format (.sbn)shape format (.shp)shape index format (.shx)geospatial metadata (.xml)
For Further Reference!
Author:Paul Bolstad