I am working on a project to look at wildlife movements from one site to another. In between the two sites is an urban area. I am trying to graphically show what habitat remains that might allow wildlife movements between these two sites. I have the Tiger/line census data, and maps of vegetation and land ownership. Manifold 4.5 (with service pack 4) so far is doing a wonderful job of displaying the basic data. 

So far, I have classified the roads by surface and traffic (figuring that a 4-lane highway has much more impact on wildlife movements than a jeep trail, etc.). I am considering adding buffer zones to these roads to illustrate estimated impact. This I know Manifold can do. What others have done for these types of studies is to plot road density (using Tiger/line roads) within a fairly tight grid, say 100m by 100m (using Arcinfo or Arcview with spatial analyst). I'm sure this will be possible in release 5, but is there anyway to do something similar in 4.5? What I would really like to do is plot housing density, but with the census data, it looks like I am limited to census blocks, which don't make sense for this purpose, given the relatively small population of the area (35,000).

In Manifold 4.5, is it possible to set up a grid system that would allow me to calculate road density? (and if yes, how?)

We think all this can be done in 4.50. See, for example, the "grid analysis" screen shots in  http://www.manifold.net/images/gallery/stpete.html  

The problem is that TIGER/Line has linear features whereas it's easiest to use points for grid analysis.  The TIGER/Line road lines must be chopped up into segments and then the lengths of all segments within each grid box is totaled up.

Doing grids is easy in Manifold. Use the tool to create grids from the Shapes toolbar. Make a 100 x 100 grid or whatever you need to cover your area. From then, the problem is figuring out how to convert the linear features into something that's countable within each grid. For example, you could create a grid of lines and then use Topology Factory to split the road lines at each intersection with the grid lines. You'd now have a bunch of road pieces. You could create a new field, Length, and then place in that field the computed length of each segment. Add of the lengths of all segments within each grid area (make the grid as areas as well) and put it in the area and you'd have a reasonably proxy for density.

Note that we lose the little line segments in between the boxes. This should not matter since all we need are relative densities within the boxes.  Why did we have to build a checkerboard grid?  We did this to avoid the need to use Topology Factory.  For $45, it's worth getting!

Other tricks: see also the Polygon in Polygon topic for "polygon in polygon" methods.