Dissappearing lines at large scales

[Eric Lam]

Hello list,

I have a set of line geometries(roads) which I am using mapserver to 
display graphically. The problem I am currently having is that certain 
lines appear at low scales (zoomed in) but not at large scales (zoomed out).

Is there a reason for this. I know that running a Douglas Peuker 
algorithm over these lines would remove them [or at least make them too 
small to see...]. Is this what is happening? Can I turn it off?

Thanks
Eric