The California Surveyor - CLSA

Report To GIS
Task Force
Editor's Note : In 1990 CLSA introduced legislation
on CIS/LIS. That legislation was
modified to create a statewide Task Force to
review and make recommendations on CIS
standards and use within the State of California.
The Task Force represents a number
of state agencies, federal agencies, universities,
counties, cities and interested associations.
Howard Brunner was appointed by the
Governor to represent CLSA. Howard recommended
and Joe was appointed to the Data
Development Technical Advisory Committee.
The following are some excerpts from
Joe's report to the Task Force. This report
discusses in detail the implications of CIS
systems to surveyors and recommends
specific guidelines for implementation in
CIS. Although this is a technical report to the
Task Force, it contains valuable information
for surveyors who are assisting local agencies
to establish CIS or are having to provide
data to agencies for use within a CIS/LIS.
The lead State agency in CIS/LIS is the
Teale Data Center. Although not an agency
surveyors are used to dealing with or have
even heard of, it is positioned to be the
dominant force in CIS/LIS for the State of
California. See the article "The Stephen P.
Teale Data Center" on page 23 for an
overview of this agency.
By Joseph W. Betit, PLS
Legal Considerations for
Information Providers
Surveyors think in terms of reliably
transmitting information related to
land and property rights over long
periods of time (often generations)
and in terms of liability to their direct
client as well as possible third
parties subsequent in time to the
original performance of work.
The correctness of a map or data
is no guarantee against misinterpretation
or misapplication of data once
the data is in the hands of others.
GIS are dynamic systems and the
inevitable changes made to the
database over time create an environment
for errors to occur and
propagate, unlike a paper map that
is a static data product. Furthermore,
if data is sold in any format (paper,
digital, etc.) as a product (versus
delivered to a sole client for their
sole use) and the data is subsequently
found unsafe or dangerous
for its intended use, United States
product liability laws provide for
strict liability for the seller of the
product. There is case law in which
inaccurate graphic representation of
accurate text data contained on the
same chart was cause for substantial
damages. In a GIS environment this
would be similar to an inaccurate
map composition being plotted along
with the accurate data tables on the
same sheet.
The current approach in law today
is to name anyone even remotely
connected with a complaint by a
plaintiff and thereby force the reluctant
defendants to fight or buy their
way out of litigation. This is an expensive
process, especially for the
innocent professional. If a licensed
professional seems overly anxious
about possible legal repercussions
from the performance of work or
delivery of product to other than the
immediate client it is for good reasons
based on hard experience with
our legal system.
Measurement Database
Focus vs
Coordinate Focus
Coordinates change, measurements
don't. Coordinates are a reflection in
a desired ellipsoid or projection system
of the currently selected or available
reduced survey measurements
contained in a database. Measurements
between two points are often
of variable quality (depending on
measurement instrumentation used).
These differences in quality are indicated
by the magnitude of the Standard
Error (SE) attribute associated
with each data element.
The most practical way to build
large survey nets for GIS systems is
to use an evolutionary approach
based on a measurement database
that undergoes periodic least squares
adjustment. The general plan for the
net should include a timeline for
long term remonumentation,
monumentation densification and
measurement upgrades.
Periodic readjustments of a measurement
database will result in new
coordinate opinions for existing
points. Therefore, the following items
should be recorded in the database
lineage log as a part of the adjustment
record; the time and date of
the adjustment, the person supervising
the adjustment, the type of
adjustment (least squares is not the
only rigorous methodology), the
parameters (points held fixed,
datum used, etc.).
Coordinate based systems are subject
to the following problem areas:
1. Flexibility in representing
information accurately in
different coordinate systems
can be difficult, especially if
the desired coordinate system
is not directly related to the
initial coordinate datum (eg.
NAD 1927 vs NAD 1983).
It is much easier to regenerate
new coordinates in the actual
new ellipsoid model from
raw measurements than it is
to try and use a transformation
program that uses best
fit techniques.
2. The coding scheme for
attribute data used to track
changes can become cumbersome
as coordinate values
are updated over time.
3. Integration of coordinate data
sets from diverse sources
may require cumbersome
translation or transformation
techniques, as well as rubber
sheeting in order to be
integrated with the coordinate
data within the existing
(different) coordinate
reference system.
Some of the derived products of a
measurement database:
• Generate parcel descriptions
directly.
• Generate annotations typical
for each type of map use
automatically.
20 The California Surveyor Fall 1992