Good answers above.
If you want to find out how much tree cover is on a particular section of trail, you can see actual photos by using the
Google map of the Katy Trail.
You'll see the trail mapped out as a red line. Use the +/- controls on the left to zoom in, and you can use your mouse to "click and drag" the map as you follow the trail.
Finally, click "Hybrid" in the upper right corner. Now you are looking at actual satellite photos, so you can see which sections have lots of tree cover and which have no trees (if you zoom in close enough). Many of the satellite photos were taken during winter so that roads would be more visible, but you can still pretty well tell where the trees are, even without leaves. If you lose track of the trail (the red line), just zoom out until it shows up.