New answers tagged algorithm
Try "STATEFIPS = 1 OR STATEFIPS = 12". Your current expression is effectively "(STATEFIPS = 1) or (12)", and since "12" will always evaluate to true this results in all features being selected.
To help with the "proper definition" part of your question; you have looked at https://en.wikipedia.org/wiki/Convex_hull and gotten what could well be considered a "proper" definition but found it lacking, so perhaps a more "useful" definition For every point inside a convex hull, a straight line to any point not within the hull will only intersect the hull ...
Vince's comments led me to look again at Shapely in Python, and it can do it. In short, the method I used was: get the bounding box of the page/object you want calculate the diagonal of this box, as this will be the minimum length your hatch lines need to be draw a square array of horizontal lines centred on the bounding box's centre, each spaced suitably ...
I think this post in the SAGA GIS forum might prove useful in answering your question about how slope is calculated: https://sourceforge.net/p/saga-gis/discussion/354013/thread/27ecdc6b/ Also, based on my understanding of TWI (as a PhD hydrology student involved in hydrologic modeling), the D-Inf (Tarboton), MFD-md (Qin), DEMON (Costa-Cabral), and MFD ...
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