NAME¶
llsearch - Search a GNIS file for place names within a given block of
latitude/longitude
SYNOPSIS¶
llsearch [-L] | [latitude_low longitude_low latitude_high longitude_high]
DESCRIPTION¶
The U.S. Geological Survey supports sites on the Internet with Geographic Names
Information System (GNIS) files. These files contain lists of place names,
complete with their latitude/longitude and other information. There are
separate files for each of the U.S. states, and each file contains many, many,
many place names. If you want to use this data with
drawmap, it is
useful to reduce the data to only the items that you need.
Llsearch
lets you filter a GNIS file and winnow out only those place names that fall
within the latitude/longitude boundaries that you specify. (You may want to
specify boundaries that are a tiny bit larger than what you are interested in,
so that numerical quantization doesn't eliminate locales that fall exactly on
your boundaries.)
Latitudes and longitudes are positive for north latitude and east longitude, and
negative for south latitude and west longitude.
Llsearch expects you to
enter them in decimal degrees. (The latitudes and longitudes in the GNIS file
are in degrees-minutes-seconds format, followed by 'N', 'S', 'E', or 'W'.
However, there are two available file formats, and one of the formats also
contains the latitudes/longitudes in decimal degrees.) Typical usage is as
follows:
- gunzip -c california.gz | llsearch 33 -118 34 -117 >
gnis_santa_ana_west
If you enter the "-L" option, the program will print some license
information and exit.
Once you have reduced the data to some subset of interest, you can search for
particular items via the
grep or
perl commands, or other search
commands, or you can simply edit the results with your favorite text editor.
Search commands are useful in reducing the sheer volume of data to a more
manageable size (by extracting, say, all mountain summits or all streams), but
you will probably ultimately end up looking through the remaining data
manually. The individual records contain codes, such as "ppl" for
populated places, and "summit" for mountain tops, that can help you
pick and choose.
There is considerable redundancy in place names, and human intelligence is
useful in sorting things out. While I was writing
drawmap and
llsearch, I frequently gazed out my office window, where I could spot
at least two, and possibly three Baldy Mountains. There are also quite a few
Beaver Creeks, Bear Canyons, Saddle Buttes, and Springfields out there. By
taking a close look at the information associated with each place name, you
can find the particular locations that interest you.
SEE ALSO¶
drawmap(1)