Quality control for land base and facilities conversion
Quality contorl procedures
The QC process includes review of hard copy plots of land base and facilities data and subsequent
reviews of digital data provided by the conversion contractors. An overview of the QC process is
outlined in Figure 1 and described below. Hard copy review is completed first for a delivery group and
digital review is completed after acceptance of hard copy plots.
Review of Hard COPYCheck plots
Hard copy review is primarily performed to verify feature content, identi~ missing features, review
quality of linework, check annotation placement and content, and determine overall map quality and
appearance. Digital orthophotos are checked for image clarity, contrast, distortion or any other defects
which could impact the visual quality of the image. Check plots are used for the hard copy QC. The
Contractor is required to submit check plots for each map sheet in the delivery group. There are check
plots for each type of digital product:
- Digital orthophoto plot
- Planimetric features plot
- Planimetric and topographic features plot
- Water facilities plot
- Sewer facilities plot
Check plots are produced on a map sheet basis at a scale of 1“= 100’. The check plots are produced in
color to assist reviewers in identi~ing features. The check plots are then marked by reviewers with
comments that are marked on the outside boundary of the check plot in an orderly fashion. The hard
copy review is performed as follows:
1. Preliminary Review
Upon receipt of check plots, the Commission reviews the plots to ensure that they are sufficiently
legible and complete, and are plotted according to the acceptable standards using the required scale
and sheet format. Once legibility has been determined, the check plots are logged into the GIS
quality control status tracking application and assigned for review.
2. Digital Orthophoto Review
The digital orthophoto plots are checked primarily for image clarity, contras$ image distortion or any
defects that could impact the visual quality of the image, such as cloud shadows, misalignments, or
dirt. Adjacent orthophoto plots are checked for uniformity of color representation, contrast, and
clarity. If there are any problems with image quality, the digital orthophoto plot(s) are returned to
the contractor with written documentation of the problems. The contractor is responsible for the
correction of digital orthophotos and is required to submit another series of hard copy check plots for
review. If any problems with the rectification of the orthophotos are evident, the entire delivery
group is rejected.
3. Detailed Planimetric Data Review
The orthophotos are used to check the planimetric data using a light table overlay where the
planimetric plot is registered to the digital orthophoto to veri~ the general feature content. Precise
registration is verified during the digital QC checks. When planimetric features on the photo image
that have been designated in the database design are not captured, corrections are noted on the check
plot. To streamline the feature checking procedure, the QC reviewer checks features on a block by
block basis. Small check marks are placed next to each feature to keep track of areas on the check
plot as they are examined. Street centerlines are checked for their continuity and to ensure that they
are joined at intersections and represent a schematic geometric center of streets. Symbology, general
appearance and quality of graphic features are reviewed, specifically smoothness of lines and
absence of unnecessary spikes, jags, or wobbles. Finally, annotation is examined to ensure that
features requiring annotation according to the database design have the correct character style and
size. Annotation content is compared with a known source to ensure that features are labeled
accurately. Street and place names are checked using sources such as existing 100’scale maps and
the City of Bostons’s Street Index.
4. Detailed Topographic Data Review
The topographic plots are examined for crossing contours, contours out of sequence, unusual spikes
that protrude from contour lines, and correct Iinestyles for the various types of contour lines (e.g.
index contours and depression contours). Areas that are checked carefhlly are large flat areas such as
parking lots, or large building footprints. These are generally areas that have been leveled off during
construction and should be represented as such by the contour lines. When the contour
representation across an area is suspect, the representation can be checked by referring to the original
aerial photos. By using a stereoscope to examine the stereo pair associated with the area in question,
topographic representation on the check plot can be evaluated. Further evaluation can be
accomplished by reviewing the DTM data. Plots of DTMs can also be requested, if necessary. Edits,
which the contractor subsequently makes to the contours, should be reflected in the DTM data.
Topographic annotation is also checked for index contours. For its placement, labels should be
“stacked” at appropriate points, and they should not interfere with planimetric features. As with the
planimetric plot, the QC reviewer examines the topographic check plot block by block to efficiently
cover the entire map sheet and ensure that all features are checked.
5. Water and Sewer Facilities Data Review
A light table overlay method is used to compare the water and sewer system check plots with the
original source maps. As with the pkmimetric check plot, small check marks are placed next to each
feature to keep track of the pipes and appurtenances that have been checked. The plots are checked
to ensure that all features on the source maps are captured in the digital data, and the alignment of
pipes and appurtenances are checked against the source maps. There is a significant amount of
annotation on the facility maps and it must be captured correctly. The annotation check is done with
the check plot and the source map side by side, and each annotation block is also marked with a
small check as it is compared to the corresponding annotation on the source maps.
6. Designation of Check Plots
The Commission determines the designation of each completed check plot in accordance with the
four possible acceptance criteria described above. It is possible that an orthophoto can be rejected
for aesthetic reasons and the planimetric and topographic features still be accepted for the same map.
If either the planimetric or the topographic plot are rejected, this constitutes an overall rejection of
the planimetric or topo data. Both pkmimetric and topo data must be accepted to designate the map
sheet as accepted. As long as the digital orthophoto is adequate to support planimetric compilation,
then the orthophoto can be rejected and the planimetric and topographic features can still be
accepted. The complete transmittal back to the Contractor is prepared with the result and required
action indicated for each map sheet in the delivery group.
Review of Hard Copy Confirmation Plots
The Contractor corrects all the errors indicated on the check plots and submits confirmation plots when
requested to do so. A confirmation plot is sent to the Commission along with the original check plot so
that QC reviewers can specifically verifj that the indicated errors have been corrected.
As with the check plots, the confirmation plots are given a designation of one of the four acceptance
categories described earlier. Confirmation plots are only rejected if corrections are not made as noted on
the check plots. Confirmation plots are returned for corrections if the requested corrections are not made
satisfactorily. The plot is accepted if all the indicated errors have been corrected. If it is determined that
the contractor did not carry out the corrections to an acceptable level or new errors are introduced or new
errors are present that were not in the original check plot, the confirmation plot is returned to the
contractor for corrections.
Performing Digital QC
After the hard copy QC has been completed for an entire delivery group, digital QC is performed on the
delivexy group. The purpose of digital QC is to verifi digital orthophoto tone and contrast, planimetric
and facility feature coding errors, edgematching, correct topology, data structure, and compliance with
the database design. Two applications (one for land base data and another for facilities data) were
developed in GDS to check that all the features were captured according to the database design. Figure 2
shows an example of one of the GDS QC application menus. A description of the components of the two
QC applications follows:
1. Digital Orthophoto ReviewBoth color and monochrome versions of the digital orthophotos are checked visually on the screen
for tone and contrast. The edges are checked against the map sheet grid to ensure proper alignment
and the planimetric features are checked for accurate registration. The orthophotos are also checked
for image distortion and mosaicking with the adjacent orthophoto. The hardware zoom and pan
fi.mctions are used to zoom in on ground features such as pavement or water edges to check for
registration errors between the vector data and the digital orthophotos.
2. Specifications CheckAll the features which have coding errors are displayed and queried to determine the coding error. A
plot of the features with wrong codes can be generated, if so desired. A report that lists the features
that do not correspond to the database design in terms of coding, line style, or character style is
created, and the features that do not conform are assigned error codes, such as ERO (objects) or ERI
(items).
3. Predetermined DisplaysPredetermined feature displays are required for the more detailed feature checks to be performed.
All features are drawn in white on the screen. Subsequent choices from feature selection sets will
overlay the white background with colored line representations on a feature by feature basis. This
function of the QC application allows the users to query any features that do not get drawn in
response to the correct feature code, or features that do not get drawn at all. For example, if the user
specifies that “wetlands” features to be drawn in blue on top of white planimetric features, and some
“wetlands” remains white rather than turning blue, the user will recognize that those “wetlands”
features have received incorrect codes. This differs from the land base specifications check since a
feature code might be a valid code according to the database design, but the code is inappropriately
assigned to the individual feature (e.g. the miscoded “wetlands” features are queried and it is
discovered that they have been accidentally coded as “river”).
4. Data Structure and Topological Checks
The QC applications provide selections to check for required topology in the data and to highlight
any situations where the structure of the digital data is inappropriate. For instance by assigning a
special linestyle to line features, such as pipes, small ticks can be created at every vertex to show
where some vertices exist in the middle of a straight section of pipe or to illustrate sections where
vertices need to be added.
Another function of the QC application allows the user to check the connectivity of lines. This is
important for checking the water and sewer systems and street centerlines. Lines to be checked are
displayed, then the user is prompted for two points along the network of lines. The program traces a
line between the two points and beeps if no connecting path can be found.
Another selection is to shade all topologically structured polygons, such as buildings and parking lots
to ensure that these have been assigned topology as required.
5. Edit Calls
The QC applications have fimctions designed to indicate errors on a GDS drawing (called an ERR
drawing) that overlays the GIS data. The user is provided with a set of menu selections that provide
tools to quickly indicate Wd describe errors on the ERR drawing. First the user must specify which
752?drawing is being QC’d in order to set a label which refers to that drawing, then the user can choose
from an assortment of tools which indicates a feature or defines an area that needs to be corrected.
Another fimction produces an error report listing all the features that have been assigned wrong
codes. Both the error report and the ERR drawing are provided to the contractor for making
corrections to the digital data.
