GIS mapping of the New York City sewer system

Background information about the New York City sewer system
The New York City sewer system is a complex network:
more than 6,000 miles of sanitary, storm, and combined pipes
200,000 manholes
14 sewer treatment plants
thousands of additional underground chamber structures

Managing the sewer system with decentralized paper maps.
Each of the City’s five boroughs has a unique method for storing and maintaining its own sewer maps and records.
There are schematic, not detailed, and not up to date paper borough-wide maps
This complicates standard infrastructure maintenance, asset management, planning and engineering tasks
Because all of the source information is stored on hardcopy media, the maps are difficult to update, or in some cases, are not maintained at all.

The advantages of a GIS:
reduced dependence on the fragile original-source documents
enhancement of planning and engineering analysis
centralization of data maintenance
advanced spatial modeling capabilities such as network traces and flow analysis would be available using a topological sewer network.

Issues related to the GIS implementation
Managing the logistics of a complex conversion from paper to digital
· More than 200,000 maps were scanned to create digital images of the paper maps
· The features of the sewer system were digitized
· The attributes for each of the 444,000 features were populated totaling approximately 10.3 million attribute values
· Quality assurance is conducted to ensure the integrity of the data

Although the investment in GIS is considerable, its development is essential to effectively maintain the infrastructure of the aging system,
and to lessen the risk of future calamity.