GIS Databases

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FOR 220 Aerial Photo Interpretation and Forest
Measurements
Lecture 20 GIS Database Acquisition, Creation,
and Editing and Analytical Processes
Bettinger and Wing (2002) Chapter 3
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Measurements
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GIS Database Acquisition, Creation, and Editing
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GIS Database Acquisition
How can GIS databases be acquired?

• Over the Internet (free)
• Through an "ftp" connection (free)
• From another organization (free?, on tape, CD,
  or ftp)
• From a consultant (, on tape or CD)
• Create a database in house

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GIS Database Acquisition
Four General Situations Exist When Needing to
Perform a GIS Analysis
(1) GIS databases required for a specific
project do not exist. (2) GIS databases exist,
but were created for general uses, and may
not be quite appropriate to address the
issues related to a specific project. (3) GIS
databases exist, but were created for other
specific projects, and are not quite
appropriate to address the issues related to
a specific project. (4) GIS databases
exist, and are adequate and appropriate to
address the issues of a specific project.
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GIS Database Acquisition
Information Associated with a GIS Database
Acquisition
GIS database requested (theme) Location
(Township/Range/Section, Topographic quad index
number (or name)) File format (e.g., Spatial
Data Transfer Standard (SDTS), ArcInfo export
format) Map projection / coordinate system /
datum Delivery method (CD, tape, e-mail, FTP,
etc.) Database compression format (None,
Zipped, MrSID, TAR, etc.) Billing
information Product license agreements
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GIS Database Acquisition
Example Internet Sites - Gifford Pinchot
National Forest (Washington State)
http//www.fs.fed.us/gpnf/forest-research/gis/ Ve
ctor GIS databases are available in ArcInfo
(ESRI, 2001) export format. Databases can either
be downloaded directly from this web site, or
obtained on a compact disc or 8 mm tape,
yet the cost of obtaining the data by this
method is 40. Some metadata related to each
GIS database can be accessed through this web
site. The data related to the forest trail
system, for example, indicates The source
scale was 124,000. It was last updated in
1999. The projection system is Transverse
Mercator, using the Clarke 1866 spheroid.
The coordinate system is the UTM system. The
datum is NAD 27. The data units that GIS
users will see are represented in meters.
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GIS Database Acquisition
Example Internet Sites - Minnesota Planning
Land Management Information Center
http//www.lmic.state.mn.us/chouse/ County-level
digital orthophotographs are available with a 10
m spatial resolution. Some metadata related to
the orthophotographs is also available. In
addition, we find that The coordinate
system is again the UTM system. The
ellipsoid is GRS80. The datum is NAD 83.
The data units that GIS users will see are also
represented in meters.
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GIS Database Creation
How can GIS databases be created?
(1) Traditional digitizing (2) Heads-up
digitizing (3) Scanning (4) As a result of
spatial analysis operations
All GIS data must be converted to a digital form.
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GIS Database Creation
GIS data sources
Digitizing the conversion of spatial information
to computer-readable form. Can account for
60 or more of the time and energy spent on GIS.
(1) Traditional method using a digitizing
table. Very precise Very accurate Requires
registration locations (tics)
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GIS Database Creation
GIS data sources
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GIS Database Creation
GIS data sources
Tic Mark Coordinates (Lat long)
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GIS Database Creation
GIS data sources
Closure / Snapping threshold
Error?
Error!
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GIS Database Creation
GIS data sources
(2) "Heads-up" method (on-screen
digitizing). Very precise Not as
accurate Requires a GIS database that has
already been registered.
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GIS Database Creation
GIS data sources

• (3) Scanning.
• Not as precise
• Not as accurate
• Requires registration locations (tics)

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GIS Database Creation
GIS data sources
(4) As a result of spatial
operations. Very precise Very
accurate Requires a GIS database that has
already been registered.
Example Create streams layer for ownership
(clipped).
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GIS Database Editing
How can GIS databases be edited?
(1) Add new features (points, lines, polygons)
to an existing database. (2) Change the shape
or position of existing features. (3) Add new
fields (columns) to the tabular database
(attribute table). (4) Edit data in existing
fields (columns) in a tabular database.
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GIS Database Editing
Maintaining topology
Topology Explicit spatial relationship between
elements. Possible with vector data structure,
not with raster.
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GIS Analytical Processes
Queries Buffering Clipping Erasing
Overlays
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GIS Analytical Processes
Queries

• Ask questions about GIS databases
• Where are the older stands?
• Which roads are paved?
• Which trails are authorized?
• Which water sources are within a given distance
  of a road?

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GIS Analytical Processes
Queries
Where are the thinnable stands? Age ? 30 and Age
? 40 Age ? 30 and Age ? 40 and MBF ? 9
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GIS Analytical Processes

• Structured Query Language (SQL)
• Uses standard operators
• e.g. gt lt -
• and or not
• Standard order of operations
• add/subtract before multiply/divide
• use parentheses to isolate terms

Example Select stands greater than 30 acres with
grass understories and a mean quadratic diameter
less than 20 inches. Query for above (area gt
30) and (understory grass) and (QMD lt 20)
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GIS Analytical Processes
Queries
Which water sources are within a certain distance
of a road?
We need more information. Perhaps a new database
layer. Buffering may help answer this question
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GIS Analytical Processes
Buffering

• Defining closed areas (polygons) within a certain
  distance of selected
• landscape features
• What do the riparian buffer zones look like?
• How far around an owl nest location is 70
  acres?
• What do the visually sensitive areas around
  trails encompass?

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GIS Analytical Processes
Buffering
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GIS Analytical Processes
Buffering
Buffering streams
Before buffering
After buffering
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GIS Analytical Processes
Buffering
Buffering owl nest locations
Before buffering
After buffering
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GIS Analytical Processes
Clipping

• Acquiring GIS data within a certain geographic
  extent.
• Need a "cookie-cutter"
• What stands are in the North Zone of the
  McDonald-Dunn forest?
• What streams are within the South Zone of the
  forest?
• How much land area is within riparian zones?
• How much timber volume is within riparian zones?

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GIS Analytical Processes
Clipping
Which roads are within the ownership boundary?
Before clipping
After clipping
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GIS Analytical Processes
Erasing

• Acquiring GIS data outside of a certain
  geographic extent.
• Need an "eraser"
• What stands are outside the North Zone of the
  McDonald-Dunn
• forest?
• What streams are outside the South Zone of the
  forest?
• How much land area is outside riparian zones?
• How much timber volume is outside riparian
  zones?
• Erasing is the functional opposite of
  clipping (which may be
• thought of as erasing outside selected
  feature(s).

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GIS Analytical Processes
Erasing
What would the stands database look like after a
land sale?
Potential land sale area
Property after erasing land sale area from the
stands database
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GIS Analytical Processes
Overlay Operations

• Processes involving two (or more) layers
• Merging is a simple overlay process that combines
  two or more layers into one. It leaves
  overlapping regions and does not create new
  attributed polygons where there is overlap.
• Three overlay processes are considered here
• Union
• Intersect
• Identity
• In contrast to a simple merge, each of these
  operations will produce a new layer with unique
  combinations of the input database polygons.

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GIS Analytical Processes
Overlay Operations
Laying one GIS database on another to produce a
combination of the two. Union Determining
the combination of two GIS databases. Resulting
GIS database will extend as far as both
input GIS databases extend.
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GIS Analytical Processes
Overlay Operations - Union
Laying one GIS database on another to produce a
combination of the two. Union What is the
combination of the stands and the fire area?
Input GIS database 1
Output GIS database
Input GIS database 2
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GIS Analytical Processes
Overlay Operations
Laying one GIS database on another to produce a
combination of the two. Intersect Finding
the overlapping areas between two GIS databases
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GIS Analytical Processes
Overlay Operations - Intersect
Laying one GIS database on another to produce a
combination of the two. Intersect Where do the
stands and the fire area overlap?
Input GIS database 1
Output GIS database
Input GIS database 2
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GIS Analytical Processes
Overlay Operations
Laying one GIS database on another to produce a
combination of the two. Identity Determining
how one GIS database can be modified by the
position of features in another. Limited to
the spatial extent of the first GIS database.
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GIS Analytical Processes
Overlay Operations - Identity
Laying one GIS database on another to produce a
combination of the two. Identity Where does
the fire occur in the stands database?
Input GIS database 1
Output GIS database
Input GIS database 2
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What county is this?
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Vector or Raster?
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Vector or Raster?
Where is this?
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Vector or Raster?
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