GIS Lecture 6
Digitizing
GIS 1
Outline
•Digitizing Overview
•Digitizing Sources
•GIS Features
•Creating and Editing Shapefiles in ArcView
•Spatial Adjustments
•Conclusion
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 2
Digitizing Overview
GIS 3
Why Digitize?
•New maps
•Map features are wrong
•Missing features
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 4
Heads Down Digitizing
•
Digitizing table or tablet
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 5
Heads Up Digitizing
•
•
Mouse on a screen
Digitizes paper maps, aerial photos, or
other images
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 6
Digitizing Sources
•Orthophotos
•GPS
•Paper Maps
•Scanning
•Raster to Vector Conversion
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 7
Orthophotography
• Digital imagery in which distortion from the camera angle
and topography have been removed, thus equalizing the
distances represented on the image
• Can be used to measure true distances
• http://gis.esri.com/library/userconf/proc95/to150/p124.html
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 8
DOQQs
•Digital Ortho Quarter Quadrangles
•Produced by the U.S. Geological Survey
(USGS)
•Grayscale or color-infrared (CIR) images
•1-meter ground resolution;
•Cover an area measuring 3.75- minutes
longitude by 3.75-minutes latitude,
approximately 5 miles on each side
•Referenced to the North American Datum of
1983 (NAD83) and cast on the Universal
Transverse Mercator (UTM) projection.
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 9
Image Resolutions
The amount of detail found in one pixel of the
image.
•image with one meter resolution means that
each pixel in the image represents one square
meter on the ground.
30 meters
10 meters
5 meters
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 10
Image Resolutions (Continued)
2 meters
1 meter
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 11
Resources
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GIS 12
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 13
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 14
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 15
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 16
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 17
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 18
Resources (Continued)
Google Maps
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GIS 19
Resources (Continued)
Google Earth
GIS 20
GPS
•Department of Defense built the global
positioning system (GPS) in the 1970s
•Network of up to 24 satellites in earth orbit
•Opened it up to civilian use in the 1980s – free
of charge
•GPS uses triangulation from signals from the
satellites
•Base stations are fixed receivers that help GPS
signals get accuracy within 1 to 5 meters
GIS 21
GPS (Continued)
•Easy to input GPS data into GIS
•GPS is most valuable when there are no base
maps sufficient to guide drawing new features
GIS 22
National Spatial Reference
System
• National network of control points (small brass disks with
identifiers and marks) placed on permanent structures
such as concrete posts
• National Geodetic Survey (NGS) establishes the known
points
• Surveyors take measurements (angles and distances)
from known locations to accurately locate points and
boundaries
• By the early 1990s, GPS became the dominant method for
establishing control points
• Some cities maintain their own points
GIS 23
National Spatial Reference
System
City of Pittsburgh control point benchmark
GIS 24
Paper Maps
Historic Maps
• http://www.usgsquads.com/svcs_historic_maps.htm#Historic
• http://digital.library.pitt.edu/maps/
-Historic maps of Pittsburgh and Allegheny County from
1872-1939
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 25
Scanning Paper Documents
•Scanned maps and images become
vectors
•Special software needed
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 26
Raster to Vector Conversion
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 27
Raster to Vector Conversion
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 28
GIS Features
GIS 29
Points
•Nodes
-Single points
-Alone or at endpoints of lines
1
2
3
node
0
0
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 30
Points
•
Vertices
- Control the shape of lines
1
2
0
3
node
vertex
0
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 31
Points
•
Tics
- control points used to register the map to the
geographic space
1
2
0
0
3
node
vertex
tic
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 32
Lines
•Connected Nodes and Vertices
•Single or multipart features
1
2
node
0
0
line
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GIS 33
Lines
FNODE_ TNODE_ LENGTH
STREET_ STREET_ID FNAME
LEFTADD1
LEFTADD2
RGTADD1 RGTADD2
180
129 595.106800
201
51635798 Kirkpatrick 605
699
600
698
From Node
To Node
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 34
Line Features with Vertices
FNODE_ TNODE_ LENGTH
STREET_ STREET_ID FNAME
LEFTADD1
LEFTADD2
RGTADD1 RGTADD2
180
129 595.106800
201
51635798 Kirkpatrick 605
699
600
698
Vertex
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 35
TIGER LINE Files
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 36
TIGER Street Centerlines
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 37
TIGER Street Centerlines
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 38
Polygons
•Closed lines
• Single polygons or multipart features
(e.g. Hawaiian islands can be multiple
polygons as one feature)
4
1
3
2
node
0
0
polygon
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 39
New Shapefiles
GIS 40
Creating New Shapefiles
•Create new point, line or polygon shapefile in
ArcCatalog
•Add Spatial Reference Information (optional)
•Add New Shapefile in ArcMap
•Edit shapefile to add features and attributes
•Stop editing
•Save edits as part of new shapefile
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 41
New Shapefiles - ArcCatalog
•
Cannot create shapefiles in ArcMap
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 42
Add Shapefile in ArcMap
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 43
Heads Up Digitizing
• Add base layers if necessary
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GIS 44
Heads Up Digitizing
• Add Editor Toolbar
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GIS 45
Heads Up Digitizing
• Start Editing
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 46
Heads Up Digitizing
• Begin Digitizing
• Click Sketch Tool
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 47
Heads Up Digitizing
• Start Drawing Points
GIS 48
Heads Up Digitizing
• Stop Editing
• Save Edits
GIS 49
Heads Up Digitizing
• Add attribute information
GIS 50
Editing Shapefiles
GIS 51
Lines and Polygons
• Advanced editing tools
-Editing Vertices
-Snapping Functions
-Multipart Features
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 52
Editor Toolbar
Editor Toolbar Sections
- Editor drop-down
- Sketch tool
- Tasks
- Target
- Attribute Inspector
- Sketch properties
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 53
Sketch Construction Tools
Sketch tool:
• Use to create point features and to digitize the
vertices of line or polygon features.
Intersection tool:
• Creates vertex at place where two segments
intersect
Arc tool:
• Creates a segment that is parametric (true)
curve. Only has two vertices as endpoints
Midpoint tool:
• Define the location of the next vertex by on two
points - the vertex is place at the midpoint of the
line between these points
End Point Arc tool:
• creates true curve by defining the start and end
points of the curve, then define a radius
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 54
Sketch Construction Tools
Tangent Curve tool
• Creates segments that are tangent
Distance-Distance tool
• Creates a point or vertex at the intersections of two
distances from two other points
Direction-Distance tool
• Like distance-distance tool except second point
uses a direction from a known point to define a
bearing line
Trace tool:
• Create segments that follow along existing
segments
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 55
Tasks
• Most features are
created and modified
through sketches
• Tasks define what you
do with a sketch
• Create features
• Modify features
• Reshape features
• Other edit tasks
• Custom tasks
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 56
Target Layer
• Target layer determines to
which layer a new feature
will belong
• Can edit multiple layers in
an edit session
•Subtypes are also listed*
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 57
Spatial Adjustments
GIS 58
Spatial Adjustments
•Transform
•Rubbersheet
•Edgematch
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 59
Transforms
• Convert data from one
coordinate system to
another.
• Converts data from
digitizer or scanner units
to real world
coordinates.
• Shifts data within a
coordinate system, such
as converting feet to
meters.
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 60
Rubbersheeting
• Geometric distortions
commonly occur in
source maps.
• They may be introduced
by imperfect registration
in map compilation, lack
of geodetic control in
source data, or a variety
of other causes.
• Rubbersheeting corrects
flaws through the
geometric adjustment of
coordinates.
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 61
Edgematching
• The edgematching process
aligns features along the
edge of one layer to
features of an adjoining
layer.
• The layer with the less
accurate features is
adjusted, while the
adjoining layer is used as
the control.
• Attribute transfer is
typically used to copy
attributes from a less
accurate layer to a more
accurate one.
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 62
Spatial Adjustment Example
• Hamburg Hall Building
Drawn in CAD
• Spatially Adjusted to
Aerial Photo
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 63
Summary
•Digitizing Overview
•Digitizing Sources
•GIS Features
•Creating and Editing Shapefiles in ArcView
•Spatial Adjustments
•Conclusion
•More to Explore
-Tutorial 6 (Introduction to Digitizing)
-On-line Help (Advanced Topics)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 64