John,

I am not sure, but here are the differences:

Mine:  500X500, PNG8, 32.4 KB
Yours: 500X350, GIF8, 65.0 KB

I'm guessing it has something to do with probably a combination of 
various things:

1) the compression algorithm
2) the color lookup table sizes
3) your have larger text and a shadow text and these and possibly you 
are using truetype antialias will cause a significant area of your map 
to not compress well.

You can very the effect of 3) by commenting out your annotation in the 
mapfile and see what happens. For 1) switch the image type to PNG8 and 
see what happens. Beyond that, I would defer to some of the other image 
experts on the list.

-Steve

ps: forward this to the list, I have been blocked from posting, 
temporarily I hope.

John Bolster wrote:

> Dear Steve,
> 
> I was looking at your Tiger Data Browser and I noticed that for roughly the
> same image size, with roughly the same features drawn, your map image is
> somewhere in the region of 12K whereas mine is nearly 70K. Any ideas how
> that could be? Here are the urls I used to compare:
> 
> Yours:
> http://imaptools.com/tiger/?PREVIOUS_MODE=1&txtZoomFactor=2&ROSA_CMD=ZOOM_IN
> &PrevStateKey=BBOX%3D-83.1391875%2C27.10938125%2C-82.137234375%2C28.11094375
> %7CSRS%3Dproj%3Dlatlong%7CMAPSIZE%3D500%2C500%7CLAYERS%3D0%2C1%2C2%2C3%2C4%2
> C5%2C6%2C7%2C8%2C9%2C10%2C11%2C12%2C15%2C16%2C17%2C18%2C19%2C20%2C21%2C22%2C
> 23%2C24%2C25%2C26%2C27%2C28%2C29%2C30&NotFirstLoad=1&RosaMode=0&INPUT_TYPE=&
> INPUT_COORD=263%2C302&QueryString=&mainmap.x=239&mainmap.y=242
> 
> Mine:
> http://www.sunnydaysmarketing.com/cgi-bin/mapserv?map=sdm.map&mapext=-82.656
> 573+27.359223+-82.656573+27.859223&mode=map&map_projection=proj=sinu,lon_0=-
> 82.656573&layers=counties+places+statelines+hwy+native+water+misc
> 
> Thanks for any hints you might have on this.
> 
> John Bolster
>