Outline
Digitizing overview
GIS features
Digitizing features
Advanced digitizing tools
Spatial adjustments
Digitizing sources
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Why digitize?
New maps
Map features are wrong
Missing features
Other?
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Digitizing tablets Used to digitize
hard copy maps into GIS
Transform wire intersections into coordinates of the tablet’s coordinate system
Heads down digitizing
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Steps for heads down digitizing Tape map to the
digitizer Register control
points on the map Estimate two
conversion equations (one for vertical and one for horizontal coordinates)
Digitize vectors (points, lines, or polygons)
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Control points
Map
Puck
Tape
Heads up digitizing Mouse on a screen Digitizes paper maps, aerial photos, or
other images
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Points
Single features
Nodes Line endpoints
Vertex points Controls shapes of lines
and polygons
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Creating points
Heads up digitizing Single point features Sketch tool and snapping features
Points added as XY event files Points geocoded using addresses
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Lines Starting and ending points with shape
vertices as needed
Vertex points
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Lines Physical attributes of TIGER streets
Shape From and To attributes
Node Address Lat/long
Length
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Polygons Three or more lines joined to form a
closed area
Single polygons or multipart features (Hawaiian islands can be multiple polygons
as one feature)
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0
0
1 2
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Creating Feature Layers or Shapefiles in ArcMap
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Within ArcMap:
-Locate an existing data layer that is similar to the layer that you wish to create.
-Start editing the existing layer, then digitize the new feature
-Select the new feature
-Export the selection to a shapefile
-Add the shapefile- fields already present and map projection is already defined -Examples in the instructor exercise
Digitize new features Create base map Add feature in ArcMap Start editing (Editor toolbar) Digitize feature Stop editing and save
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Specify angle and length
Lines and polygons
Straight segment tool
Type length and angle
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Snapping tools
Snapping toolbar
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Point Snapping
Endpoint Snapping
Vertex Snapping
Edge Snapping
Generalize tool Creates features for use at small scales
with less detail while preserving basic shapes
U.S. Census cartographic boundary files
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Census TIGER water feature City planning rivers
Smooth tool Smoothes sharp angles in polygon
outlines to improve aesthetic or cartographic quality
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Smooth before Smooth after
Cut polygons Creates two polygons from one original Cut polygon tool
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Polygon before Polygon after
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Transforms Converts data
from one coordinate system to another. from digitizer or scanner units to real world
coordinates.
Shifts data within a coordinate system, (e.g. feet to meters).
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Rubbersheeting Geometric distortions commonly occur
in source maps may be introduced by imperfect registration in map
compilation lack of geodetic control in source data variety of other causes
Corrects flaws through the geometric adjustment of coordinates
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Edgematching Aligns features along the edge of one
layer to features of an adjoining layer
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.
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Spatial adjustment example Hamburg Hall CAD Drawing
CAD drawings generally do not have geographic coordinates
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Spatial adjustment example Spatially match drawing to map using
displacement links
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USGS
United States Geological Survey
Common Data Types & Standards Digital Elevation Models (DEMs) Digital Orthophoto Quads(DOQQs) Digital Line Graphs(DLGs) Digital Raster Graphics (DRGs) Landsat Satellite Images Land Use Land Cover (LULC) Spatial Data Transfer Standard(SDTS)
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Orthophotography Digital imagery in which distortion from
the camera angle and topography have been removed, thus equalizing the distances represented on the image
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Digital Ortho Quarter Quads—DOQQs
http://online.wr.usgs.gov/ngpo/doq/ 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
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DOQQ image resolutions The ground length of 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 meters30 meters 10 meters10 meters 5 meters5 meters
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National Elevation Data Sets United States Geological Survey
(USGS) National Elevation Dataset (NED) Shaded Relief Imagery Data (Free)
Maps provide highest-resolution elevation data available across the United States, in raster format
http://ned.usgs.gov/
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Scanning paper documents Raster to vector conversion Paper (historic) maps Scanned maps and images become
vectors Special software needed
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