Digitizing and Analyzing Data

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 non-spatial 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?

Digitizing and Analyzing Data