Calculate slope aspect in relation to polygon

Question

I have a proposed lot plan for a new subdivision.  I'm trying to find which lots slope away or slope towards the streets - essentially uphill and downhill.  I also need to classify the lots by slope categories (0-5, 5-10, 5>10%).

I took my surface and calculated the slope and the aspect.  I reclassified the aspect into general directions and the slope catagories I need.  I spatially joined my lot polygons to these rasters.

I have polygons defining my streets and I've buffered them so that they overlap my lot polygons. What I am having trouble with is determining the slope direction off of the street polygon.

I'm assuming I need to assign elevations to my street polygons and then do a comparison between the elevations and slope of the lot polygons but I'm not sure how to do that.

AngelaLivingston · Answer

I think I figured it out with the help of both of you.  I clipped my streets to the lot polygons.  Converted them to points and assigned elevations to them from the surface.  I did the same thing for the lots.  Then I used field calculator to populate the difference in Z's between the two point classes.  If the streets were higher, then I marked the lot as downhill slope.  And vice versa.

Thank you for the help. Much appreciated!

FC_Basson · Answer

I think you are on the right track.  You've already calculated the aspect and sloped per subdivision and created street buffers to see which street the subdivision intersects with.  I would then clip the street buffers with the subdivisions and calculate the center points for the subdivision polygon and the street buffer clip polygon.  With the Generate Near Table tool (Advanced licence only: Toolbox -> Analysis -> Proximity -> Generate Near Table) you can generate a table using the two center point data sets with information about the direction from the subdivision center point to the street buffer center point. Then you can compare the subdivision slope with the point-to-point angle.  This process might not work in all cases, but give I would give it a try.

DanPatterson_Retired · Answer

were your streets on the dem? I would assume that you have polygon bounds representing the lots, so you could do a tabulate area or zonal statistics as table to get the slope and azimuth for the lots... of course this is predicated on the assumption that the lots are already prepped for development making the elevations and their derivatives meaningful

Tabulate Area—Help | ArcGIS for Desktop

Zonal Statistics as Table—Help | ArcGIS for Desktop