How does GIS work?
Data storage
The ArcGIS Interface
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Copyright © 2006 by Maribeth H. Price
Vector model
Polygon
Vertices
Points
Line
Nodes
Y
Features are
stored as a
series of x-y
coordinates
in a
rectangular
coordinate
system.
Many
different
coordinate
systems may
be used.
X
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Copyright © 2006 by Maribeth H. Price
Features linked to data
Each feature is
linked to an entry
in a data table
containing
information about
the feature.
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Copyright © 2006 by Maribeth H. Price
Advantages of vectors
•
•
•
•
•
Precise location of features
Storing many attributes
Flexible for cartography
Compact storage of information
Ideally suited for certain types of analysis,
especially areas, lengths, connections
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Copyright © 2006 by Maribeth H. Price
The raster data model
X, Y
location
X, Y
location
Columns
Rows
Raster data file
N rows by M columns
Georeferenced to earth’s
surface
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Copyright © 2006 by Maribeth H. Price
GIS data models
Vector model
Raster model
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Copyright © 2006 by Maribeth H. Price
Digital Raster Graphic
Converting Vector to Raster Data is
Easy
Converting
Raster
Data to
Vector is
Hard
Impossible
Types of raster data
Discrete raster: land use
Discrete raster: roads
Continuous raster: DEM
Continuous raster: image
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Copyright © 2006 by Maribeth H. Price
Some Common Image Formats
• JPG – Used for most digital photos but
“lossy.”
• GIF – Best for line drawings. 256 colors
maximum. No loss
• TIF – Standard in many technical
applications. No loss
• PNG – Lossless image format
• RAW – Data as captured by digital camera
Continuous data
• Raster is the best way to
store continuously
changing values such as
elevation
• Analysis faster and more
flexible than vectors for
many applications
• Some analysis only
possible using rasters
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Copyright © 2006 by Maribeth H. Price
Raster analysis functions
Distance
Interpolation
Density
Least cost path
Viewshed
Buffers
Copyright © 2006 by Maribeth H. Price
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Impact of resolution
90m resolution
10m resolution
• Storage space
increases by the
square of the
resolution
• Portraying large
areas at high
precision is
problematic
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Copyright © 2006 by Maribeth H. Price
Storage of attributes
Raster contains 1 value
indicating a single attribute—
road type for example
• Roads may have other
attributes: ownership,
speed limit, number of
lanes, etc.
• Would need a new
raster for each attribute
• Only numeric attributes
may be stored
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Copyright © 2006 by Maribeth H. Price
The raster data model
X, Y
location
X, Y
location
Columns
Rows
Raster data file
N rows by M columns
Georeferenced to earth’s
surface
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Copyright © 2006 by Maribeth H. Price
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Copyright © 2006 by Maribeth H. Price
ModelBuilder
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Create models built from sequences of tools
Store processing steps for later reference
Execute models repeatedly with different inputs
Share models with others
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Copyright © 2006 by Maribeth H. Price
Extract spot
elevations every 50’
for 11 input datasets
bh_c.shp
Discard out-of-boundary
spot elevations
WS0607-outlet
4model.shp
Document Location
of Known Outlets
Contour2point_clip.shp
Export to
delimited text
Input01.txt
Final Spot Elevations
In x,y,c Format
Final
Spot Elevations
Boundary Of Area
To Be Modeled
WS0607Culvert.shp
Thinned And
Combined Township
Spot Elevations
“Thinned” Elevation Data
Township
2-Foot Contours
WS0607Boundary.shp
Contour2point_bhc.shp
Contour2point_all.shp
Merge 11
datasets
Hydrologic modeling
furnished by Door County
Soil and Water
Conservation Department
Moonlight Bay
Basin.shp
Flow path.shp
Calculated Flow Paths
Dataset
Analytical Operation/
GeoprocessingTool
Copyright © 2006 by Maribeth H. Price
* aka “Hidden Brook Subwatershed”
Hwy 57
Basin.shp
Mud Lake
Basins.shp
South Outlet*
Basin.shp
Calculated Subwatershed Boundaries
THE RIDGES SANCTUARY
WATERSHED STUDY - 2006-2007
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Geospatial Analysis - Summary Flow Diagram
Revision Date: 10 September, 2007
By: Mike Stiefvater