Evaluating Alternative Line Simplification Strategies for Multiple Representations of Cartographic Lines

Two basic strategies have been identified for handling multiple representations of line features in digital databases. Either a finite number of scale-dependent representations of cartographic lines can be explicitly stored, or a scale-independent database is generated from which subsequent scale representations can be extracted as needed. These two strategies parallel differences in hierarchical and non-hierarchical line simplification operators. Non-hierarchical line-simplification can produce the most geometrically accurate simplification at any scale, while hierarchical operators are often associated with scale-independent databases. In this research, hierarchical and non-hierarchical line simplification operators are evaluated by comparing both the points retained by these different algorithms and the overall quality of the graphic portrayal for sample lines of different complexity and at different scales. Visual inspection of the results did not reveal any discernable difference at any scale for any line. Subsequent numerical analyses shows some differences but overall little geometric quality is lost by using a hierarchical operator as opposed to a non-hierarchical one and given the greater flexibility of scale representations that is possible, hierarchical methods appear to be more satisfactory.