[Mapserver-users] Coloring shapefile layer according to DBquery

[Randy James]

Hi 

I have a 30mb shape file i converted to postgis and found
that once it was indexed it was faster than when i was
using it as a shape. But on the other hand it may have been
faster for small areas if i tiled it as a shape file and
than loaded it.

Cheers
Randy


 --- Steve Lime <steve.lime at dnr.state.mn.us> wrote: > A DBF
file is part of a shapefile- the part that holds
> the attribute
> information. I'm not sure
> whether PostGIS or local shapefiles are faster, my guess
> is the latter
> but not overwhelmingly
> so.
> 
> Switching entirely to Postgres is not a downgrade, rather
> an upgrade
> (you wouldn't
> need the "build the shapefile" step. However, you'd have
> to move away
> from MySQL or
> at least run both in parallel and try and keep them in
> sync. Worse than
> the shapefile 
> option in my opinion.
> 
> Building custom data isn't sexy but it's often a reality
> that nets you
> great performance.
> 
> Steve
> 
> >>> "Matthew Haines" <mhaines94108 at hotmail.com>
> 10/10/2003 3:50:06 PM
> >>>
> 
> So which is faster, reading the shapefiles from the DBF
> file or
> (assuming I 
> move to PostgreSQL) reading them from a PostgreSQL
> database?
> 
> Reading between the lines I'm guessing that (1) the .DBF
> files are an 
> indexed database file, (2) mapserver has an XBASE
> database engine built
> in, 
> and (3) XBASE is the fastest database for this kind of
> application, and
> 
> therefore (4) switching to MySQL or PostgreSQL would be a
> form of 
> downgrading.
> 
> Precompiling everything isn't quite as sexy as doing
> doing it on the
> fly, 
> but speed is very important, and not having to add
> PostegreSQL to my
> server 
> and migrate everything from MySQL is also good.
> 
> Matthew
> 
> ----Original Message Follows----
> From: "Steve Lime" <steve.lime at dnr.state.mn.us>
> To:
>
<mhaines94108 at hotmail.com>,<mapserver-users at lists.gis.umn.edu>
> Subject: Re: [Mapserver-users] Coloring shapefile layer
> according to
> DBquery
> Date: Fri, 10 Oct 2003 15:11:54 -0500
> 
> An increasingly popular topic these days.
> 
> There is no way with CGI MapServer to link the two for
> map creation.
> Your best bet
> would be to create a custom shapefile that combines the
> base shapefile
> and the MySQL
> database. You can use MapScript and the DBD drivers for
> MySQL and
> XBase
> to do this
> pretty easily. The psuedo code is something like:
> 
> - copy the base shapefile to a new file
> - open the new shapefile DBF file
> - add the new columns
> - open the connection to MySQL
> - for each shape select the corresponding MySQL row
>    - copy the content from MySQL to the DBF file
> - close everything
> 
> Really shouldn't be more that 20 lines.
> 
> If done properly you could run this script every so often
> to sync the
> 2
> datasets using cron. The advantage of this approach is
> that it gives
> you a dataset
> optimized for map making. The real time joins are
> certainly doable but
> would absolutely
> kill performance- that's why they're not supported.
> 
> If your MySQL data is not changing every few seconds then
> this
> approach
> should work
> quite well. Postgres/PostGIS is of no help unless you
> want to move
> everything into it and
> not use MySQL.
> 
> Steve
> 
> Stephen Lime
> Data & Applications Manager
> 
> Minnesota DNR
> 500 Lafayette Road
> St. Paul, MN 55155
> 651-297-2937
> 
>  >>> "Matthew Haines" <mhaines94108 at hotmail.com>
> 10/10/2003 2:20:18 PM
>  >>>
> 
> I have a shapefile for the tax lots in Manhattan (New
> York City) and I
> have
> a lot of information about the individual tax lots in a
> MySQL
> database.
>   I
> would like to generate maps where I color the tax lots
> according to
> the
> data
> in the MySQL database.
> 
> Just as an example, I have a table that tells me how many
> residential
> units
> have been built on a particular tax lot.  I might like to
> color the
> map
> by
> population density so that single family dwellings are
> light red, 2-4
> family
> buildings are medium red, and 5+ family apartment
> buildings are dark
> red.
> 
> Is there any way to do this without loading the shapefile
> polygons
> into
> the
> database?  I've had several thoughts, but they seem
> impractical ...
> 
> => I could use Perl MapScript to write a program that
> would scan the
> entire
> database table and assign tax lots to different layers
> ... but there
> are
> 100,000 tax lots in Manhattan and that might take a long
> time.
> 
> => I could try to get put the data into the shapefile ...
> but how?  I
> don't
> have any commercial mapping software for working with
> shapefiles.  Is
> there
> a utility to do this?  Also that makes my data hard to
> update.
> 
> => Is there a MAP file command to load data from a
> database and
> somehow
> join
> it to the shapefile on the fly so I can define layers
> based on it?
> 
> I'm hesitant to mess with MySQL, if only for fear of
> breaking my
> existing
> applications.  The documentation indicates that the MySQL
> connector is
> 
> buggy.
> 
> What's the best way to go about this?  Do I have to
> install
> PostgreSQL?
> 
> Pointers much appreciated,
> 
> Matthew
> 
> Matthew
> 
> 
=== message truncated === 

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