onlyhuman,
I’ve mapped out routes on mapmyride.com and found it to be a useful toy, but it has its limitations. When it comes to measuring gradients I think that the resolution isn’t fine enough to be fully accurate, that is also reflected in the total ascent calc which seems to always be on the low side.
Other than that I like it.
I have a rule of thumb for working out how hard a ride is going to be. I simply divide the height climbed in metres by the distance travelled in kilometres. This gives me an index number that is an indication of how intense the route is. All I then have to decide is if I think that I can manage the distance.
Over a period of time I’ve also noticed that (unsurprisingly) my average speed for a route trends along with the intensity, but in the opposite direction – the more intense, the less speed.