Quality control for land base and facilities conversion
Mohammad Tariq
Program Manager (GIS), Boston Water and Sewer Commission
425 Summer Street, Boston, MA 02210
David Koehler
Sr. Research Analyst,Pkmgraphics, Inc.
1300 Spring Street, Silver Spring, MD 20910
Abstract
One of the key factors in timely and successfi,d implementation of an AM/FM/GIS is the establishment
of quality control procedures for reviewing and accepting products from conversion contractors. The
Boston Water and Sewer Commission implemented uniform quality control (QC ) procedures for
inspection of hard copy and digital products to ensure confidence in the accuracy of the land base and
facilities GIS databases being developed. The hard copy and digital data are checked to confirm content
and positional accuracy of graphic features, adherence to the database design, correctness of attribute
data, annotation, topology and overall consistency and completeness of the databases.
Introduction
The Commission is responsible for providing water and sewer and storm drainage services in the City of
Boston. The City encompasses approximately 45 square miles of area and according to the 1990 US
census has a residential population of 574,283, plus an additional daytime population of 480,000. The
Commission owns and maintains approximately 1,340 miles of sewers, including 535 miles of sanitary
sewers, 490 miles of storm drains, and 315 miles of combined sewers, and a number of other facilities,
including pumping stations, tidegates and regulators. All wastewater generated in the city is transported
to the Massachusetts Water Resources Authority (MWRA) treatment facilities located at Deer Island in
Boston and Nut Island in Quincy. The Commission also owns and maintains approximately 1,182 miles
of water mains. Water for the City of Boston is purchased from the MWRA at an average of about 90
million gallons per day. There are currently 85,500 customer accounts.
The majority of the Commission’s maps and data regarding water and sewer facilities are in paper
format. Existing water and sewer-related information is maintained on 100’and 50’ scale maps. These
maps, drawings and related data are updated and revised manually.
The Commission’s major objectives in establishing an AM/FM/GIS are to:
- Develop an efficient means of maintaining up-to-date water and sewer system maps and data
bases.
- Develop and maintain a single, centralized source of facilities information which is easily
accessible to all departments.
- Develop a means of sorting, processing, manipulating and storing facilities information.
The Commission is implementing AM/FM/GIS in a phased approach. Phase 1 involved a feasibility
study to investigate current and fiture operations dealing with geographic data which would benefit from
the use of AM/FM/GIS technology. During Phase 2, Graphic Data Systems (GDS) software was selected
by the Commission as its GIS, and a data conversion pilot project was conducted for two neighborhoods
of the city. As part of the pilot project, the water and sewer facilities data was filly developed and
prototype applications were implemented. Based on the results of the pilot, a full-scale automated
mapping, facilities management and geographic information system is currently being implemented as
the final phase. During this phase a new land base is being developed from aerial photography taken
during the spring of 1995 and water and sewer facilities maps are being converted to a digital format.
The Commission has contracted for the development of a new land base map and production of digital
orthophotos and for conversion of existing water and sewer facilities maps which are registered to the
new land base data. The Commission is using a very comprehensive quality control (QC) process, which
includes review of hard copy plots of land base and facilities data and subsequent reviews of digital data
provided by the conversion contractors. This paper summarizes the quality control (QC) process used by
the Commission to check the quality of products delivered by the conversion contractors.
Database Development Activities
Land Base Mapping
new land base is being created from aerial photography taken during the spring of 1995. The land base
data includes development of 1“= 100’scale digital planimetric and topographic data as well as digital
orthophotography. The production of land base data required the acquisition of color aerial photography
at 1”= 600’ scale taken from an altitude of 3,600 feet, and establishment of horizontal and vertical photo
control and aerotriangulation.
The planimetric features such as transportation, hydrography, buildings, wetlands and other land features
have an accuracy of +/- 2’. These land base features are stereocompiled from the aerial photography
described above. The digital orthophotos have a pixel resolution of 1 foot. The topographic data
includes 2’ contours and spot elevations derived from a Digital Terrain Model (DTM).
Facilities Conversion
The Commission’s existing 1“= 100’scale water and sewer maps are used as the primary source for
conversion of facilities data to digital format. The facilities data is registered to the new land base map
developed from the aerial photography, as described above. The facilities data includes graphic data as
well as attribute data stored in an Oracle database.
Delivery of Products
The city is divided into 12 areas for the delivery of data. The map sheets associated with these areas are
called delivery groups. The delivery groups generally contain 23 map sheets. Deliveries occur on a
monthly basis. The planimetric, topographic, and digital orthophoto data is being completed prior to the
start of the facilities conversion effort. The same delivery groups apply for both the land base data
deliveries and the facilities data deliveries.
Acceptance criteria of Delivered Products
A QC review is performed by the Commission for each delivery of products by the contractor. After QC
review of the check plots, confirmation plots or digital data, the Commission determines the status of the
product according to the following list:
All the products which have systematic errors that impede the review are rejected. The cause of
rejections are typically:
- A class of features is missing from plot
- Plot quality is poor
- Overall line quality is unacceptable
- An error, such as miscoding of features, is repeated more than 15 times
Rejected products are not completely reviewed by the Commission. The Contractor is required to
resubmit the rejected products in same form.
Corrections Required
The QC reviewers make comments for corrections during QC review. These comments maybe on check
plots, confirmation plots, or digital data, depending on the stage of the review. In case of check or
confirmation plots, the comments for corrections are placed directly on the plots. In the case of digital
QC, comments are annotated on a digital GDS drawing which overlays the relevant digital drawing files.
In response to these comments, the contractor is required to submit a confirmation plot or new digital
data at the Commission’s discretion.
The Commission accepts the submittal of the product. This authorizes the contractor to submit digital
data. If the acceptance is of digital data, then the product is filly accepted.
Accepted/BWSC Edit
The Commission determines that required corrections are minor enough to accept the submitted product,
however any errors noted will be corrected by the Commission staff once the entire digital delivery
group is accepted.
