Final Class Project by TCW

Unlike previous class projects, semi-complete "cook book" instructions were not provided. Instead, only goals and hints were provided to encourage a student lead project specific GIS design and implementation. Questions were encouraged and the class message board was well utilized. Weekly submittals were required to make sure that each group remains "on target".

The final project is based on historical maps of Charlottesville, Virginia copyrighted by the Sanborn Map Company in 1920. According to the lesson background section:

From the late 19th century through the 1990s, the Sanborn Map Company authored what are arguably the most information-rich maps of urban America. The original intent of the maps was to provide a risk assessment tool to the fire insurance industry. They have come to be an important resource in all kinds of research settings, including urban geography, architectural history and preservation, urban planning, ethnic studies, urban archaeology, genealogy, and many others.

Figure 1: Example Sanborn Map (1920_03a)

Because of their intended purpose, the most detailed aspect of the maps are the buildings. Looking at a Sanborn map, one can find information on construction materials, number of stories, entry-ways, ownership, street address, general (residential, commercial, public) as well as specific building type (office, warehouse, garage), and sometimes the date of construction. Other kinds of information that can be gleaned from the maps include street names and widths, land elevations, utility lines, parks and railroad tracks.

The final project premise states that the Albemarle County Historical Society (ACHS) located in Charlottesville Virginia intends to create GIS data layers from 20th century Sanborn maps to aid in land use change studies, genealogy, and visualization of their city. A proposal has been requested for a GIS that includes layers depicting 10-year intervals from 1900 through 1990. This final class project has our group of four "GIS practitioners" competing for the large contract by designing and implementing a pilot GIS project based on just two Sanborn maps (supplied in four scanned images: 120_02a.jpg &120_02b.jpg, plus 120_03a.jpg & 120_03a.jpg.) Thirty scanned map images were supplied so no two students were assigned the same image. Note: According to the map index, the city population was 15,000 in 1920. According to the US Census, the population had grown to 45,049 in 2000.

Technical Procedures A proposed work flow was submitted on the 2nd week of the Final Project. The workflow listed many of the individual steps in a tutorial fashion. Only the major steps are outlined here. Additional detail is included in the next section (QA/QC). Sanborn Maps Georeferenced - Each Sanborn map needs to be located in space and warped to best fit the surviving landmarks that are most visible on the orthorectified photo. Adjust Map Images with an image editor (such as PhotoShop) - The rectified map images can usually benefit from some pixel level manipulations that sharpen edges and improve contrast. Digitize and Attribute all Five layers / Feature Classes - This is the most work. Use the Sketch Tool..... Combine Everyone’s Work - Use the ArcMap geoprocessing wizard to "Merge layers together". Repeat for each feature class. Edge Match - Map objects that span multiple Sanborn maps will require adjustment because of less than perfect alignment. Edge Data Check - Check for missing and duplicate map objects along the Sanborn map boundaries. (Delete duplicates and add missing map objects.) Merged Data Check - Sort and run queries against the merged attribute tables looking for problems. Edit Attribute Data - Use the Microsoft Access table column Find/Replace action to make the data more consistent. Generate Attribute ID numbers - VBA code was developed using Microsoft Access to populate the attribute tables. Export the Feature Classes as Shape Files - Use the ArcToolbox. For possible data use by ArcView 3.x Project Shape Files to GCS_North_American_1983 - ArcView 3.x is limited to a Geographic Coordinate System

Error-Checking and Error Correction Quality assurance/quality control procedures (QA/QC) for the proposed project will follow a plan of data entry, visual inspection, and standard queries to test for errors of entry and database structure. Data entry tasks include heads up digitizing of lines and polygons and keypunch entry of attributes for the same lines and polygons. The primary data source for the pilot project is 30 Sanborn map images from 1920. Data captured consists of street centerlines with address ranges, building footprints with addresses, heights, and use category, rail lines, Sanborn map extents, and municipal block footprints. Individual and groups of maps will be digitized by more than one technician and fitted together in a final mosaic for each decade. Attributes will be added by each technician at the time of digitization. Our pre-bid feasibility study used four technicians who each digitized one map. Only the street centerline and building footprint tasks were implemented. QA/QC began at the digitization stage by careful attention to detail by each technician. Independent error checking began at the merge stage as the individual contributions were assembled into a working prototype GIS. The following procedures where employed for each task: STREET CENTERLINES Add individual street feature classes to the same ArcMap document Use the ArcMap GeoProcessing Wizard to merge all street feature classes Start edit session, confirm, merged streets are target, and select Modify Feature as task. Set snapping to edge and vertex. Perform 100% check and correct any under or overshoots. At individual map edges, estimate a compromise junction point and adjust junctions accordingly (see Figure 3). Delete duplicate segments. Perform 100% check and confirm segment direction is consistent with address range direction. Perform 100% check and confirm validity of address ranges for each segment in attribute table. Save edits and map document then close ArcMap Open streets attribute table in Access and sort the data various ways to help look for trouble, etc. (see the queries below). Use Edit>Replace to adjust records so that spelling, capitalization, and punctuation are consistent throughout. Use VBA script to assign unique Street IDs. This approach was also used to give the Street IDs some meaning. The streets were sorted by street name and starting address before the sequential numbers were generated & assigned.

Figure 3:	Two screen shots showing: 1.) Mismatched individual street centerlines from adjacent maps, and 2.) Final compromise junction shown in red.
BUILDING POLYGONS Add individual building feature classes to the same ArcMap document. Use the ArcMap GeoProcessing Wizard to merge all building feature classes. Start edit session, confirm, merged buildings are target, and select Modify Feature as task. Set snapping to edge and vertex. Perform 20% check of vertices and polygon alignment with Sanborn map source. If error rate exceeds one in ten, repeat with an additional 20% check until overall rate is below 10%. Delete duplicate structures. Confirm validity of addresses and use for each structure in attribute table. Perform 20% check of structure heights. If error rate exceeds one in ten, repeat with an additional 20% check until overall rate is below 10%. Save edits and map document then close ArcMap Open building attribute table in Access and sort the data various ways to help look for trouble, etc. (see the queries below). Use Edit>Replace to adjust records so that spelling, capitalization, and punctuation are consistent throughout. Use VBA script to create unique Building IDs. This approach was also used to give the Building IDs some meaning. The buildings were sorted by address number and street name before the sequential numbers were generated & assigned. EXAMPLE ACCESS QUERIES How inconsistent Street names were spotted: SELECT Trim(Right([address],Len([address])-InStr([address]," "))) AS [Street Name], Count(buildings.address) AS [Count Street Name] FROM buildings GROUP BY Trim(Right([address],Len([address])-InStr([address]," "))) ORDER BY Trim(Right([address],Len([address])-InStr([address]," "))), Count(buildings.address); How the buildings were sorted before the Building_IDs were assigned: SELECT Trim(Right([address],Len([address])-InStr([address]," "))) AS [Street Name], Left([address],InStr([address]," ")-1) AS [address number], buildings.address, buildings.build_id FROM buildings ORDER BY Trim(Right([address],Len([address])-InStr([address]," "))), Left([address],InStr([address]," ")-1);
Database Error Analysis One source of error is the Sanborn Maps. We can not go back to 1920 and measure the city but we can spot inconsistencies. When the first two maps were merged together (1920_02a & 1920_2B) the alignment was disappointing. A better match was expected along 1st Street because both maps share relatively well defined landmarks for georeferencing. The intersection of Jefferson St. and 1st St. was studied closely. Both SketchTools georeferenced their map image using the same North-West corner of the city park (the South-East corner of the intersection). Differences in the georeferencing can be seen in the two screen shots below (with semi-transparent Sanborn maps shown over the modern orthorectified photo). However, the two Sanborn maps disagree with regard to east-west street alignment and widths. Map 1920_02a shows straight center-line alignment through the intersection whereas Map 1920_03a shows a noticeable offset with Jefferson St. N.W. significantly wider.

Figure 4:	Two screen shots showing the intersection of Jefferson St. and 1st St. - Map 1920_02A versus map 1920_03A
Sanborn map 1920_02A was particularly difficult to georeference because all of the potential landmarks from 1920 in the western half of the map no longer exist. Georeferencing variability was demonstrated by having a second SketchTool georeference the same map. The resulting spatial difference is demonstrated in the following figure by the different locations shown for the same buildings (in a few select cases). However, the four maps fit together well enough to aid in land use change studies, genealogy, and visualization of the city as shown in the figures.

Figure 5:	Georeferencing Error Illustrated by Comparison. - Two SketchTools georeferenced Map Image 1920_02a. Difference in the georeferencing are illustrated by offset building locations in a few select cases. The large building was the McGuffey Primary School in 1920 (now used as an "Arts Center"). The South-East corner is offset by 5.3 meters.

GEOG 5223 Final Project (Lessons 7, 8, 9 & 10)

Reconstructing 1920 Charlottesville, Virginia

by the "SketchTools" - December 2003

David Beahm, Tom Bell, John Branigan & Tom Wells

Sanborn Maps Georeferenced - Each Sanborn map needs to be located in space and warped to best fit the surviving landmarks that are most visible on the orthorectified photo.

Adjust Map Images with an image editor (such as PhotoShop) - The rectified map images can usually benefit from some pixel level manipulations that sharpen edges and improve contrast.

Digitize and Attribute all Five layers / Feature Classes - This is the most work. Use the Sketch Tool.....

Combine Everyone’s Work - Use the ArcMap geoprocessing wizard to "Merge layers together". Repeat for each feature class.

Edge Match - Map objects that span multiple Sanborn maps will require adjustment because of less than perfect alignment.

Edge Data Check - Check for missing and duplicate map objects along the Sanborn map boundaries. (Delete duplicates and add missing map objects.)

Merged Data Check - Sort and run queries against the merged attribute tables looking for problems.

Edit Attribute Data - Use the Microsoft Access table column Find/Replace action to make the data more consistent.

Generate Attribute ID numbers - VBA code was developed using Microsoft Access to populate the attribute tables.

Export the Feature Classes as Shape Files - Use the ArcToolbox. For possible data use by ArcView 3.x


Figure 2:	Charlottesville, Virginia 1920 Sanborn Index Map Showing the SketchTool's Sample Work Area