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

Error Analysis/Discussion

What are the sources of possible error when it comes to the spatial and attribute data? If the error acceptable given the purpose of the project?

Spatial Data

1. Error in georeferencing the Sanborn Maps.
2. As a result of a possible error in the spatial aspect, some georeferenced maps didn’t fit well with other ones.
3. The orthophoto could not be projected in advance.
4. The X/Y Domain should not be established correctly.

Attribute Data

1. Error in establishing the parameters oat the moment of designing the Attribute Tables of the features.
2. Specially in the streetline features, that the fields FromAddL, ToAddL, FromAddR, ToAddR should not be the correct because of the inaccurate information in the map and/or the lack of information in the map.
3. The same thing occurred in the buildings layer, where the structures’ name didn’t appear in some of them.
4. Finally, one possible error is based in Selection by Attributes, where, for instance, if we wanted to created other features to be exported to the ArcMap’s Table of Contents and there is no records to choose according to the query we could give it to specify certain criteria to export as a new feature layer, it should be possible that there is an error in the data because of a possible lack of information if we would query inexistent information in the Attribute Tables with the Selecting by Attributes function.

Is the error acceptable given the purpose of the project?

The errors for the purpose of this exercise are acceptable for a few reasons:

1. The needs of the ACHS are for historical recollection, not for engineering.  As such, the offset of a building or street does not harm the final product.  Of course, the data need be correct as provided (see point 3 below) and the maps need to illustrate the town as it was, both from how it looked and what it contained--streets shouldn't be so far off as they are not recognizable.
2. Because this is a process where we are learning how to detect errors and  fix something that could be erroneous. In other words, we were learning techniques and how to work with them. This exercise was only for academic purposes.
3. Because it is out of our own hands that there was some information missing in the map, we cannot conclude as such that it was an error that there was no data if the map didn’t have some of them to include them in the attribute tables. In other words, we could work with the existing information but not in one that there was nothing to perform.

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.