Multi-Scale Representation of a Digital Line

A scheme for multi-scale geometrical representation of a digital line is proposed. A digital line is represented as a structured object in which lines at different levels of resolution are represented as lists, quadcodes are used as control mechanism for guiding line simplification at multiple scales of a pyramid, and operators for simplification and smoothing are used to generate lines at different levels of resolution. In this scheme, lines at different levels of an image pyramid can be automatically generated without specifying the so-called tolerance value. Experimental results show that up to a certain level of resolution, the simplified lines retain important information content and recognizable characteristics. Also, the image pyramid assures a legible representation at any level of representation. Future research should improve the current line simplification operator and address the correspondence between lines at different levels of an image pyramid and the lines at different map scales.     

Fractal Enhancement of Cartographic Line Detail

In plane geometry curves have a dimension of exactly 1 and no width. In nature, all curvilinear features have width, and most have dimension greater than 1, but less than 2. Many phenomena, such as coastlines, have the same "look," even when viewed at greatly varying scales. The former property is called "fractional dimensionality," and the latter is called "self similarity." Curves digitized from maps may be analyzed to obtain measures of these properties, and knowledge of them can be used to manipulate the shape of cartographic objects. An algorithm is described which enhances the detail of digitized curves by altering their dimensionality in parametrically controlled, self-similar fashion. Illustrations show boundaries processed by the algorithm.     

Adapting Generalization Tools to Physiographic Diversity for the United States National Hydrography Dataset

This paper reports on generalization and data modeling to create reduced scale versions of the National Hydrographic Dataset (NHD) for dissemination through The National Map, the primary data delivery portal for USGS. Our approach distinguishes local differences in physiographic factors, to demonstrate that knowledge about varying terrain (mountainous, hilly or flat) and varying climate (dry or humid) can support decisions about algorithms, parameters, and processing sequences to create generalized, smaller scale data versions which preserve distinct hydrographic patterns in these regions. We work with multiple subbasins of the NHD that provide a range of terrain and climate characteristics. Specifically tailored generalization sequences are used to create simplified versions of the high resolution data, which was compiled for 1:24,000 scale mapping. Results are evaluated cartographically and metrically against a medium resolution benchmark version compiled for 1:100,000, developing coefficients of linear and areal correspondence.     

Recent Literature

Development of a temporal geographic information system (GIS) and spatio-temporal data modeling are key to incorporating time into geographic information science. This paper describes how to design and develop temporal GIS that will work with spatio-temporal data represented in various data models, and it introduces a prototype temporal GIS with a case study. In temporal GIS, the integration of multiple spatio-temporal representations is based on common spatial and temporal reference systems. In other words, a map window of temporal GIS visualizes spatio-temporal data valid at the same time within one spatial area. To achieve such visualization, separate data editing and query modules are required for each spatio-temporal data model (STDM). In the temporal query interface, after a user specifies a time, the system automatically hires correspondent modules to retrieve spatio-temporal data valid at that time. Besides temporal queries common to all STDMs, each module may provide additional temporal query capabilities specific to that STDM. In the case study, I implement a prototype temporal GIS for three STDMs. The examples of query and visualization, which use three datasets (census data, land use/land cover, and elevation data) demonstrate the prototype temporal GIS can integrate multiple temporal representations.