[Xastir] basic map question

[Tom Russo]

On Tue, Jul 24, 2007 at 10:09:28PM -0600, we recorded a bogon-computron collision of the <needhame1 at plateautel.net> flavor, containing:
>  Jason Winningham wrote:
> >
> > On Jul 22, 2007, at 1:49 PM, Earl Needham wrote:
> >
> >> - what's the difference in the polygon and the polyline maps?  Can one or 
> >> the other be deleted so I have more room on my hard drive?
> >
> > polygons are things like bodies of water, parks, etc.  lines are linear 
> > features like roads, railroads, etc.
> >
> > I've never used them separately, so I'm not sure what the results would be 
> > if you didn't use one or the other.
> >
> > I'd guess that they would be pretty much useless without the lines; I'm not 
> > sure what they'd look like without the polygons.

>  	It's just that they're so awfully slow to load from my hard drive -- I 
>  would have thought they'd almost HAVE to be faster than loading a map from 
>  the internet, but they actually take maybe 4 or 5 times as much time.

It is because of the essential difference between them.

The on-line maps are being downloaded as rendered images.  The shapefiles are
being rendered by Xastir, and each line is being read in, examined, drawn
and labeled.

For big shapefiles such as county-wide TIGER/Line data this can be very slow.
Rtree helps it somewhat (by generating a spatial index so it doesn't have to
do very slow linear searches through the data), but there's just so much
you can speed it up without doing a lot of special preparation on the data 
files (some folks here have done that).

-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM
"And, isn't sanity really just a one-trick pony anyway? I mean all you get is
 one trick, rational thinking, but when you're good and crazy, oooh, oooh,
 oooh, the sky is the limit!"  --- The Tick