Introduction to Geographic Information Systems
Spring 2013 (INF 385T-28437)
Dr. David Arctur
Lecturer, Research Fellow
University of Texas at Austin
Lecture 6
Feb 14, 2013
Digitizing
Outline

Digitizing overview

GIS features

Digitizing features

Advanced digitizing tools

Spatial adjustments

Digitizing sources

Dataset metadata
INF385T(28437) – Spring 2013 – Lecture 6
2
Lecture 6
DIGITIZING OVERVIEW
INF385T(28437) – Spring 2013 – Lecture 6
3
Why digitize?

New maps

Map features are wrong

Missing features

Other?
INF385T(28437) – Spring 2013 – Lecture 6
4
Heads down digitizing

Digitizing tablets
 Used to digitize hard
copy maps into GIS
 Transform wire
intersections into
coordinates of the
tablet’s coordinate
system
INF385T(28437) – Spring 2013 – Lecture 6
5
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)
Tape
Control
points
Puck
Map
INF385T(28437) – Spring 2013 – Lecture 6
6
Heads up digitizing


Mouse on a screen
Digitizes paper maps, aerial photos, or other
images
INF385T(28437) – Spring 2013 – Lecture 6
7
Lecture 6
GIS FEATURES
INF385T(28437) – Spring 2013 – Lecture 6
8
Points

Single features

Nodes
 Line endpoints

Vertex points
 Controls shapes of lines
and polygons
INF385T(28437) – Spring 2013 – Lecture 6
9
Creating points

Heads up digitizing
 Single point features
 Sketch tool and snapping features

Points added as XY event files

Points geocoded using addresses (CH 7)
INF385T(28437) – Spring 2013 – Lecture 6
10
Lines

Starting and ending points with shape
vertices as needed
Vertex points
INF385T(28437) – Spring 2013 – Lecture 6
11
Lines

Physical attributes of TIGER streets
 Shape
 From and To attributes



Node
Address
Lat/long
 Length
INF385T(28437) – Spring 2013 – Lecture 6
12
Polygons

Three or more lines joined to form a closed
area
4
3
1
2
0
0

Single polygons or multipart features
 (Hawaiian islands can be multiple polygons as
one feature)
INF385T(28437) – Spring 2013 – Lecture 6
13
Polygons

Physical attributes




Shape
Area
Perimeter
Length
INF385T(28437) – Spring 2013 – Lecture 6
14
Lecture 6
DIGITIZING FEATURES
INF385T(28437) – Spring 2013 – Lecture 6
15
Create new feature class

Created in ArcCatalog
INF385T(28437) – Spring 2013 – Lecture 6
16
Create new feature class

Add spatial reference information
INF385T(28437) – Spring 2013 – Lecture 6
17
Create new feature class

Add new fields
INF385T(28437) – Spring 2013 – Lecture 6
18
Create new feature class

Feature class created
INF385T(28437) – Spring 2013 – Lecture 6
19
Digitize new features





Create base map
Add feature in ArcMap
Start editing
(Editor toolbar) 
Digitize feature
Stop editing and save
INF385T(28437) – Spring 2013 – Lecture 6
20
Create base map for digitizing

Vector features or raster images
INF385T(28437) – Spring 2013 – Lecture 6
21
Add new feature class
INF385T(28437) – Spring 2013 – Lecture 6
22
Add Editor toolbar

Customize, Toolbars, Editor toolbar
INF385T(28437) – Spring 2013 – Lecture 6
23
Start editing

Editor, Start editing
INF385T(28437) – Spring 2013 – Lecture 6
24
Begin digitizing
INF385T(28437) – Spring 2013 – Lecture 6
25
Click point (tree) locations
INF385T(28437) – Spring 2013 – Lecture 6
26
Stop editing

Editor, Stop editing
INF385T(28437) – Spring 2013 – Lecture 6
27
Edit attribute data

Start editing, populate fields in table
INF385T(28437) – Spring 2013 – Lecture 6
28
ArcGIS 10.0  10.1

Note that the “Edit Vertices” toolbar has 2 new
tools not shown in the lab book exercises,
check them out:
INF385T(28437) – Spring 2013 – Lecture 6
29
Lecture 6
ADVANCED DIGITIZING
TOOLS
INF385T(28437) – Spring 2013 – Lecture 6
30
Specify angle and length

Lines and polygons
 Straight segment tool

Type length and
direction angle
INF385T(28437) – Spring 2013 – Lecture 6
31
Snapping tools

Snapping toolbar
INF385T(28437) – Spring 2013 – Lecture 6
32
Trace tool


Good for complicated shapes
Editor toolbar, Trace tool
INF385T(28437) – Spring 2013 – Lecture 6
33
Cartographic generalization
Bolstad, pg 138, Figure 4-9
INF385T(28437) – Spring 2013 – Lecture 6
34
Generalize tool

Creates features for use at small scales with
less detail while preserving basic shapes
 U.S. Census cartographic boundary files
Census TIGER water feature
INF385T(28437) – Spring 2013 – Lecture 6
City planning rivers
35
Smooth tool

Smoothes sharp angles in polygon outlines
to improve aesthetic or cartographic quality
Smooth before
INF385T(28437) – Spring 2013 – Lecture 6
Smooth after
36
Cut polygons


Creates two polygons from one original
Cut polygon tool
Polygon before
INF385T(28437) – Spring 2013 – Lecture 6
Polygon after
37
Lecture 6
SPATIAL ADJUSTMENTS
INF385T(28437) – Spring 2013 – Lecture 6
38
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).
INF385T(28437) – Spring 2013 – Lecture 6
39
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
INF385T(28437) – Spring 2013 – Lecture 6
40
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.
INF385T(28437) – Spring 2013 – Lecture 6
41
Common digitizing errors
INF385T(28437) – Spring 2013 – Lecture 6
42
Undershoots, overshoots, snapping
INF385T(28437) – Spring 2013 – Lecture 6
43
Spatial adjustment example

Hamburg Hall CAD Drawing
 CAD drawings generally do not have
geographic coordinates
INF385T(28437) – Spring 2013 – Lecture 6
44
Spatial adjustment example

Spatially match drawing to map using
displacement links
INF385T(28437) – Spring 2013 – Lecture 6
45
Lecture 6
DIGITIZING SOURCES
INF385T(28437) – Spring 2013 – Lecture 6
46
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)
INF385T(28437) – Spring 2013 – Lecture 6
47
Orthophotography

Digital imagery in which distortion from the
camera angle and topography have been
removed, thus equalizing the distances
represented on the image
INF385T(28437) – Spring 2013 – Lecture 6
48
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

Interactive DOQQ ordering:
http://earthexplorer.usgs.gov/
INF385T(28437) – Spring 2013 – Lecture 6
49
USGS EarthExplorer
INF385T(28437) – Spring 2013 – Lecture 6
50
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 meters
INF385T(28437) – Spring 2013 – Lecture 6
10 meters
5 meters
51
DOQQ image resolutions
2 meters
INF385T(28437) – Spring 2013 – Lecture 6
1 meter
52
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/
INF385T(28437) – Spring 2013 – Lecture 6
53
Scanning paper documents




Raster to vector conversion
Paper (historic) maps
Scanned maps and images become vectors
Special software needed
INF385T(28437) – Spring 2013 – Lecture 6
54
Dataset metadata

Make your data discoverable over the web
 Record what your data is about while it’s fresh!
Source: ISO 19115 – Geographic Information
Metadata Content Standard
INF385T(28437) – Spring 2013 – Lecture 6
55
Editing metadata in ArcCatalog
Be a friend to other
data users besides
yourself:
Fill in metadata
for shared datasets
whenever possible!
INF385T(28437) – Spring 2013 – Lecture 6
56
Summary

Digitizing overview

GIS features

Digitizing features

Advanced digitizing tools

Spatial adjustments

Digitizing sources

Dataset metadata
INF385T(28437) – Spring 2013 – Lecture 6
57