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Alquist-Priolo
Earthquake Fault Zones in California –
Statewide Collection in Electronic
Format
What is the
difference between the digital image CD
(e.g. CD 2000-03 Southern Region) and
GIS data CD (e.g. CD 2001-05 Southern
Region)? Digital image CDs
contain pdf files that basically are a
picture of the Alquist-Priolo Earthquake
Fault Zone (APEFZ) map. The CD can be
used in the user’s computer without the
need for purchasing additional software.
The images are viewed using Adobe
Acrobat Reader, which is supplied with
the CD. The images are not interactive.
The user can view the maps on screen, or
print selected parts of the maps at
various scales (see question regarding
printing the maps). GIS
data CDs contain files that can be
combined with other GIS data files such
as vector parcel maps. With the GIS
software, the user can perform spatial
queries, conduct statistical analysis,
and extract specific data. The user
cannot view or work with the GIS data CD
unless they have a GIS system installed
on their computer.
What is GIS?
GIS stands for Geographic
Information Systems. GIS is a computer
system for storing, integrating,
manipulating, analyzing and displaying
data related to positions on the Earth's
surface. A Geographical Information
System is used for handling maps of one
kind or another. These might be
represented as several different layers
where each layer holds data about a
particular kind of feature. Each feature
is linked to a position on the graphical
image of a map. Layers of data are
organized to be studied and to perform
statistical analysis. Potential users of
GIS data include: government agencies,
town planners, public utility managers,
environmental and resource mangers,
engineers, businesses, marketing, and
distribution.
What software programs do I need to view
the raster images? The raster
images are in pdf (portable document
format) and can be viewed using Adobe
Acrobat Reader. A copy of this software
program is included in CD 2000-03, 04,
and 05.
I
have a copy of CD 2000-03, Digital
Images of Official Maps of
Alquist-Priolo Earthquake Fault Zones of
California, Southern Region. Can I print
copies of the maps? Yes, you can
print copies of the maps. However, the
size of the original map (typical map
dimensions are about 20 inches wide by
30 inches high) will require the use of
a plotter if you want to print the
entire map at the original 1:24,000
scale (1 inch equals 2,000 feet). Using
Adobe Acrobat Reader, one can select and
print at the original scale a specific
area of the map. At the top of the menu
bar (for Adobe Acrobat Reader version 4)
hold the mouse button down on the “grab
text” tool button, which will expand to
three buttons. Chose the “grab graphics”
tool button (last one on the right).
Using this tool, select the area of
interest. Now, using the zoom box, enter
“267%” as zoom number, then copy the
selection. Using 267% will result in an
image at approximately the original map
scale (1 inch equals 2,000 feet). Paste
the image into the desired application.
Can I view the GIS
data CDs using Adobe Acrobat Reader?
No, you must have a GIS software program
installed on your computer to view the
GIS data. See next question.
What software
program do I need to view the GIS data?
In order to view and use the APEFZ GIS
data, you will need to have a GIS
software program installed on your
computer. Some typical GIS software
programs include: MapInfo, ArcView,
ArcInfo, and Intergraph.
Are base maps
included in the GIS data CDs? No,
base maps, such as topographic raster
images, are not included. The GIS data
files are intended to be used with the
users GIS base maps. For example, a
local lead agency may have a GIS system
containing data showing parcel
locations. The APEFZ GIS data can be
added to this system, assisting the lead
agency in their responsibility to
determine whether or not specific
parcels are located within an APEFZ.
What is the
projection of the GIS data files?
California State Plane Coordinate System
(SPCS) (NAD 1927). SPCS is subdivided
into regional zones (SPCS zones I –
VII).
Will the GIS data
CD allow me to determine if a specific
property is located within an APEFZ by
typing in a street address? No.
Base maps are not included with the
APEFZ GIS data and we have made no
attempt at creating software programs
that would run this type of query. The
user can determine if a property is
within an APEFZ by importing the APEFZ
GIS data as one of several data layers
which include parcel boundary layers.
Running a query with the GIS system will
allow the user to determine if a parcel
polygon is located within an APEFZ
polygon. The user should be cautioned,
however, that the original scale at
which the APEFZ maps were digitized is
1:24,000 (1 inch equals 2,000 feet) and
locations of the APEFZ zone boundaries
are no better than ±50 feet. Also see
next question.
What
is the scale that the APEFZ maps were
originally digitized from?
Original hardcopy EFZ maps were compiled
over the past 25 years at a scale of
1:24,000. GIS data files were created by
scanning the hardcopy maps used to
generate Official EFZ maps. The scanned
images were then digitized on screen.
The result is GIS files showing point,
line, and polygon features representing
annotations and registration points,
fault traces, and EFZ boundaries.
Although it is possible to show the GIS
features at any scale, users of these
digital files must recognize the
difference between precision and
accuracy. The digital data can be
reproduced precisely at any scale, but
the accuracy of the data remains
constant. As the scale is increased from
1:24,000, uncertainty and errors in
fault location and EFZ boundary and
turning point locations remain the same.
Are
the 2001 series of CD releases for APEFZ
maps updates of the 2000 series? No, the 2000 series are digital images
of APEFZ maps and the 2001 series
contain GIS files. The number of maps
and the issue dates are identical for
each series.
How can I obtain
revisions or new maps? New and
revised APEFZ maps are issued
periodically. Official maps are issued
following a 6 month review period. Both
the Preliminary Review maps and Official
maps will be announced on the CGS web
site. Revisions to existing maps or new
maps, when official, will be available
for downloading on the CGS website.
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Information Page
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