Is there anyone out there having a suggestion, a model for a solution to the following typical mapping/cartographic problem:
-Assume we have given two sets of area objects. For simplicity, let us call them L1 (large lakes) and L2 (small lakes). Also, for simplicity, let us use the topology area notion where an area is defined by one, and only one, outer (enclosing, container) border polygon and a zero or arbitrary number of inner (excluding, hole) border polygons. Anything inside a hole-polygon, just like anything outside the container-polygon, is outside the corresponding area. How L1 and L2 are created is irrelevant but they may be of huge cardinality. -Assume that there are no other than topologic relations between the elements of L1 and L2. In other words, areas from the large and small lakes may fully, almost or partly overlap; some of the holes may belong to objects in L1 and L2 at the same time, many holes only in objects from L1 but not in objects of L2 and the contrary, and so on. So, the question/problem is - find/create a new set of areas L that covers L1 and L2 but where the holes from L1 and L2 remain as holes in L? Real-world examples of this issue may be found in OSM source data. Take for the L1 lakes (or holes) from the planet_land (created from the coastline data) and for L2 lakes from the natural_water data. Whatever rendering model is used, some of the islands will disappear. Rendering a new area class over L1 and L2 will never solve the described problem. The dilemma is why some islands are present only in the coastline data but not in the overlapping natural_water data and the contrary. The described issue is obviously a problem in many OSM mapping applications. Finally, the problem might be a challenge for researchers, mappers and programmers. Note that even in a well founded theoretical solution a program should probably handle hundreds of thousands polygons and hundreds of millions vectors simultaneously. Some more detailed specification and examples you may find in a white paper here: https://docs.google.com/file/d/0B6qGm3k2qWHqemFoeXpseTlndFk/edit?usp=shari ng Regards, Sandor.
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