是否有可能满足所有这五个要求？最后一点也不是最不重要的。
1) an overlay image is placed above a base image
(e.g. push pin at specified intersection on a city map)
2) the city map can be dynamically resized by the user in the browser window
(the base image content is static -- i.e. resizing does not include more or less of the city)
3) the size of the push-pin is proportional to the size of the city map
(the bigger the city map, the bigger the push-pin; the smaller the city map,
the smaller the push-pin)
4) as the city map's size changes, the push pin's location remains accurate
5) The developer does not have to recalculate the pin's location when map's size changes