1. The problem asks for the rule to ensure a quadrilateral has a positive area. 2. A quadrilateral is a polygon with four sides and four vertices. 3. To have a positive area, the quadrilateral must be non-degenerate, meaning its vertices should not be collinear. 4. More specifically, the points defining the quadrilateral must not all lie on the same straight line. 5. Also, the shape must be simple (not self-intersecting) to have well-defined positive area. 6. Another mathematical rule: the sum of lengths of any three sides must be greater than the length of the fourth side to form a closed shape with area. 7. If coordinates of vertices are known, the area can be computed by the shoelace formula; a positive result confirms positive area. 8. Summary: A quadrilateral has positive area if its four vertices are not all collinear, it is simple (no self-intersections), and forms a closed shape with non-zero polygon area.