measure slope/plan trips on google maps

So this winter i got frustrated with the available online mapping tools and wrote a google maps mash up to help me plan backcountry trips. It gives you:

* Side by side, coordinated topo and satellite views.
* Basic slope estimates at a point.
* Overland distance and elevation gain/loss for trips (change the mode to path).
* Point forecast at weather.gov

It is still somewhat buggy but I have been finding it very useful and I just got around to posting somewhere publicly accessible (google app engine for the geeks). Check it out and let me know if you have any feedback or feature requests...I'm doing this in my spare time with zero budget but I'll try and make improvements as I can:

www.hillmap.com/

(let me know if this too spamy for TAY ... i figured it is at least on topic)

this is pretty cool - although it would be very useful to be able to draw a line and get the average slope on the line instead of at a point

Could you make it look like the images on this page:

avalanchesafety.blogspot.com/2010/10/union-creek.html

Very slick.

Any idea how accurate google maps is for estimating slope? It looks like 40' intervals.

Average Slope:
I just uploaded an update to do average slope of the last link when you put it in path mode but you may have to clear your browser catch to get it to work. This is the slope of the line that connects the two points so it doesn't consider any local roll overs or steepness transverse to the direction of the line etc.

Overlays:
I'd love to do slope overlays like that but google limits the the amount of calls you can make to their elevation service to the point i can't even do max slope along the path at a reasonable resolution. I may try and get by hands on some elevation data some other way so I can do things like that but no promisses.

Resolution:
Google doesn't publish resolution but claims that their elevation data is the best that they can get their hands on for any given area but that resolution varies. They do the interpolation and give you their estimate of elevation for the points you request.

I estimate the maximum slope by requesting points in a circle around the center and seeing which one has the biggest slope...you can adjust the radius of this circle in the settings panel to see what effect this has if you want.

So its an estimate based on estimates and I wouldn't trust it in the place of actually measuring. I have been comparing it to what I see with my compass inclinometer and it does good on open slopes but it can radically underestimate the slope of vertical cliffs (climbing not skiing terrain) and be thrown off by the walls in narrow couloirs.

Neato Ryan, that's very convenient and useful.