Most areas on the west side (West Hollywood, Culver City, Beverly Hills) and to the north (Silver Lake, Los Feliz) have very walkable areas are all relatively safe. Downtown LA still has a sketchy history but in reality is very safe these days. It's one of the places in the city where there are legitimate lofts.
A concave polygon is defined as a polygon with one or more interior angles greater than 180Â°. It looks sort of like a vertex has been 'pushed in' towards the inside of the polygon. Note that a triangle (3-gon) can never be concave. A concave polygon is the opposite of a convex polygon. See Convex Polygon. In the figure above, drag any of the vertices around with the mouse. Take note of what it takes to make the polygon either convex or concave. Also change the number of sides.
What is a Concave Wheel? Concave Technology takes the center of the wheel and dips inwards to give it that bowl effect. Rather than exaggerating a bigger lip for the back wheel, and a smaller lip for the front. Concave wheels emphasize the concavity of the rear wheel to differentiate from the front wheel.