Allow for the shape, pen, or highlighter snap feature to instinctively recognize an intersection of polygons, lines, or just a plain dot. This feature is mainly focused on imported documents and images. In the image below is a triangle (redrawn for clarity) where at each corner, the blue do for the highlighter snap shape is not at the corner. The snap tool should detect intersections, such as for a grid line or corner of a polygon, and automatically move to the intersection.