The following code implements a grid with a polygon that can have its locator points moved and finds the area of the polygon. When initially executed the area is not calculated and gives an error message. But once you click on a locator to move it or even if it stays where it is the code executes properly. Can anyone see where my error is or how to fix the code to avoid this initial error?
DynamicModule[{pts = {{5, 0}, {9, 2}, {9, 6}, {11, 10}, {4, 10}, {3,
7}, {3, 5}, {2, 1}, {3, 1}}},
Column[{
LocatorPane[
Dynamic[pts],
Graphics[{
Table[Point[{n, m}], {n, 0, 14, 1}, {m, 0, 10, 1}],
EdgeForm[{Thick, Black}], Transparent, Polygon[Dynamic[pts]]
}, ImageSize -> Large],
{{0, 0}, {11, 15}, {0.5, 0.5}}, LocatorAutoCreate -> True
],
Dynamic[Area[Polygon[pts]]]
}]
]
Thank you.