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| GeoCommunity Mailing List |
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| Subject: | Re: [gislist] Preparing Maps |
| Date: |
12/15/2005 12:05:02 PM |
| From: |
Bill Thoen |
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On Wed, Dec 14, 2005 at 09:48:23PM -0500, DickBoyd@aol.com wrote:
> ... The legend included several symbols that were not on the maps. The
> presenter explained that these symbols were on the legend because they
> appeared somewhere in the county. The only way to get the data with the
> desired data, he explained, was to prepare a map for the entire county
> and then take that county wide map and select the area to be displayed
> from that larger map.
>
> The time and cost estimates for preparing the maps seemed excessive to me.
>
> Is there a way to prepare a map with the desired attributes by specifying the
> coordinates for coverage instead of "cutting" and "pasting" from a larger
> map? Is it faster and cheaper to limit the sort earlier in the process?
Sure, but it's always easier and cheaper to specify up front what you want
the map to show. It sounds like the software used to make the maps was
using an automatic selection of objects based on the physical limits of the
map data to build a legend. It's probably not capable of building a legend
based on the limits of the view. With most good desktop GIS software, you
could write a script to automatically build a legend based on what's in the
extents of the view, and even create a list of critical sites as an
index... but apparently your mapmaker doesn't have such a tool yet.
If the mapmaker had known that you wanted the legend to show only what's on
the view or to show a view that included important nearby sites just
outside the FPD in question (such as the dynamite factory next to the
gasoline refinery, just over the one-lane bridge down the only road that
leads to the nuclear power plant) then they probably would have used either
a manual technique to build the legend (slow and expensive) or expanded the
coverage to include sites that are significant to the FPD.
> The map locating grid was latitude and longitude. Could the map have been
> prepared more quickly by sorting for the data elements of interest within
> geographic limits and then preparing the map? The geographic coordinates would have
> gone beyond the borders of the fire districts and would have included data of
> interest in the neighboring districts. The borders of the fire district would
> have been one set of data.
How does the mapmaker know what geographical limits you want? In my
experience, people usually tell me, "We want a map showing the limits of
the FPD, including historical incidents, critical infrastructure,
transportation, hydrology, ..." In the absense of other information, I
would make the map to fit the limits of the FPD, and then that affects the
scale, symbology, lables and layout of the resulting map. Changing the map
limits on an ad hoc basis and still producing a good map often means you
have to redo quite a lot of work.
But you raise an important point for anyone who makes maps for the purposes
of emergency planning. The goal is to present spatial information in a
form that helps planners plan for the real world, and jurisdictional
boundaries are not necessarily the limit of the real region of interest.
Mapmakers should ask questions about nearby features and issues and take
that information into account when laying out the map.
> The way the data was presented also suggested there may be an anomaly between
> the coordinates. The fire district seems to be defined by range and township.
> The anomaly is that about five acres seems to be "orphaned" by a lake.
I've seen FPD's orignially defined by township and range but that have
been changed over time by law to add or subtract odd bits of land for
various reasons. That's why when I make fire protection planning maps I try
to get as much of the base data from local sources, and hope that their
data are accurate. It's a lot more expensive if the mapmakers have to
research land records to discover what parcels are part of an FPD and what
are not.
> Another factor was audience response. Even though the presenter explained
> that the map was prepared for a specific audience to answer a specific set of
> questions, most of the discussion was regarding what the map was saying in the
> context of the viewers point of view and how the map could be prepared to answer
> their questions.
What was the presenter supposed to do? It sounds like what you had there
was a breakdown in communication. Either the mapmaker didn't do the right
job or the agency/person(s) commissioning the map didn't tell the mapmaker
what they really needed.
> What is the experience of the members of gislists regarding public
> participation in map presentations in briefings intended for a very specific audience?
The public generally isn't trained to evaluate risk the same way as the
professionals do. Not that the public is ignorant, but
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