Overview
Data Structure
Digitizing
Data Entry Errors
Level of Effort
Error Analysis
Metadata Report
Future Mapping

Data Entry Errors

Preventing (and correcting) data entry errors required us to pay particular attention to the three elements we created: 1) Buildings feature class, 2) Street feature class, and the data in the tables associated with the two feature classes and the look up table.

Buildings

The key for buildings was to prevent or fix polygon errors, such as overlap and loops.  A key method to avoid the problem was to use Auto Complete for polygons that shared one or more walls.  It was also very important to set the snapping options to ensure that ArcMap found the right vertex, end point, or edge to digitize to.

To fix overlaps, we can use clip or modify features.  To correct loops, we use modify features and eliminate or add a necessary vertex to fix the problem.  We update attributes as necessary.

Streets

The key to getting the streets correct included preventing or fixing undershoots, overshoots, and direction (must digitize from the From to the To!).  Again, the method of preventing these errors was to properly set the snapping options and to zoom and pan as necessary to make good points.

to fix undershoot or overlap, we use trim/extend to modify the incorrect element.  Again, it is necessary to set the snapping options to best support the operation.

Tables

The key to getting the tables correct included searching for anomalies like misspelled entries, null values, non-standard forms, etc.  Other than paying attention to the typing during the data entry phase, we use the table sort and query capabilities to find and fix problems.  Another good method is to set up a query and ask the dialog to "show all values."  This way St, St., Str., etc. show up in order and are easy to see.

Some Specific Steps to Prevent Data Entry Errors.

1. Snapping command was selected. End for roads and buildings were also used.
2. Manually check over entries and use the Sanborn map annotation for review.
3. Used snapping to get good location on data points for generating shapefiles.
4. Used trim and extend to get the street centerlines to start and stop at the centerline of the digitized street—hoping this would simplify combining the information from all four datasets.
5. Used copy and paste for some data entry so that the entry would all be the same (e.g., 1920).

GEOG 5223: Elements of GIS: Part 2 (ESRI Track) CD. Accessed September 2004.

How to Read Sanborn Fire Insurance Maps, University of Virginia Library website. http://fisher.lib.virginia.edu/collections/maps/sanborn/web/details.html.  Accessed September 2004.

GEOG 5223: Project 7, 8, 9 & 10: Final Project, Accessed September 2004.