Digitizing and Analyzing Data
Prepared by:
John McGee
Jennifer McKee
With support from:
NSF DUE-0903270
in partnership with:
Geospatial Technician Education Through Virginia’s Community Colleges (GTEVCC)
Purpose
• To learn techniques for generating new
spatial features in a layer.
• To learn techniques for including nonspatial data in your final Map Layout (for
example, graphs and reports)
New Techniques Covered
•
•
•
•
•
•
•
Working with raster data
Digitizing from digital imagery
Adding X,Y data to a map document
Buffering layers
Creating a report
Creating a graph
Adding a graph to a Map Layout
Digitizing
• Method of converting information from
one format to another using a trace
methodology.
• Traditionally, digitizing has meant the
creation of a spatial dataset from a
hardcopy source such as a paper map or a
plan.
Digitizing
• The “old way”
Heads-up Digitizing
• Uses on screen digitizing, usually with an
aerial photograph in the “background”
• You are no longer bent over a digitizing
table (hence “heads up”).
• ArcGIS provides several tools to support
editing…
Digitizing Data
• Most vector spatial data
has been digitized from
paper maps and aerial or
satellite photographs.
• Digitizing data involves
placing a map or photo
on a digitizing table and
tracing features.
– Heads-up digitizing is
digitizing on your monitor,
not a tablet.
Digitizing Without Tracing
• Features can also be digitized without
tracing.
– ArcGIS has several tools for creating circles,
rectangles, curves, and other shapes of exact
dimensions.
• You can specify angles and lengths of line
segments.
• You can specify that line segments be
perpendicular or parallel
Points
• Points are features with no parts.
– They can be digitized with a single click.
• Lines have a beginning and ending, and
often change direction.
• Polygons are lines that return to their
origin.
Endpoints
• The points where a line begins and ends is called an
endpoint.
• The points where a line changes direction or is
intersected by another line are called vertices.
• The segments between vertices are called edges.
Endpoints (in red)
Vertices (in green)
Edges
Digitized Line
Edit Sketch
• A feature that has its vertices, edges, and
endpoints visible. Once the feature is
saved, the vertices, edges, and endpoints
disappear and it is no longer an edit
sketch.
Edit Session
• All digitizing is done during an edit session.
– Task: operation you want to carry out
– Target: layer in which features are being digitized
– Tool: software function for completing the task
Tools
• 9 Tools for drawing edit sketches
– Grouped on a drop-down tool palette called the
Sketch Tool
Sketch Tool
Sketch Tool
• Creates new features within point, line, and
polygon layers
Sketch Tool
Midpoint Tool
• Lets you define the location of the next vertex by
clicking two points; the new vertex is placed at
the midpoint of the line between these points.
– Example → Roads
Midpoint Tool
Distance-Distance Tool
• This tool lets you create a point or vertex at the
intersection of two distances from two other
points.
– Creates two circles based on two distances and finds two possible
intersection points where the primary can be placed.
Distance-Distance Tool
Direction-Distance Tool
• Allows you to create a vertex using a distance from a
known point, plus a direction from a known point to
define a bearing line.
– For example, a pole might be located at a specified distance from
the corner of one building, and at a defined angle from the
corner of another building.
Direction-Distance Tool
Trace Tool
• Helps you create new segments that follow
along existing segments.
– Essentially creates parallel line segments
Trace Tool
Tangent Curve Tool
• Adds a segment that is tangential to the previously
sketched segment.
– This tool is practical when sketching rail lines in which the
curves are nearly always tangential to the previous segment.
Tangent Curve Tool
Arc Tool
• The Arc tool helps you create a segment that is a
parametric (true) curve.
Arc Tool
Intersection Tool
• The Intersection tool creates a vertex at the place where
two segments would intersect if extended far enough.
Intersection Tool
Endpoint Arc Tool
• Allows you to specify the start and endpoints of the
curve, then define a radius for the curve.
– This is particularly useful in sketching cul-de-sacs, where the
beginning and ending points of the arc, as well as the radius of
the cul-de-sac, are known.
Endpoint Arc Tool
Undo Mistakes
• You can undo digitizing mistakes with the
Undo button on the Standard Toolbar.
• Or you can use ctrl-z
Questions?