UNIFORM MODEL OF THE ORGANIZATION AND REPRESENTATION OF DIGITAL TOPOGRAPHIC MAPS AND PLANS
Work with GIS demands qualitative digital topographical bases which make basis of a spatial data uniform infrastructure. Now there are different principles and methods of digital topographical map and plan compilation (DTMPC), and also various ways and forms for realization of these models. As a whole the situation with digital topographical bases in the Russian market is as follow:
- Existing data are diverse both on structure and on ways of coding the topographical information; therefore there is a problem of compatibility the data received from different sources;
- The approach to DTMPC as to simple reproduction of paper maps prevails. Such data are aimed first of all at reproduction of the paper original and do not consider to the full specificity of work in GIS.
- Digital topomaps and topoplans through display the same objects, are created by the different rules which often have been not coordinated with each other
In DATA+ works on creation of the unified objects model of vectorial DTMPC, orientated first of all on technical opportunities of work with such data in GIS for a number of years are conducted. On the basis of acting in given area domestic and international standards the logic model of data which defines principles of formal representation of terrain objects in GIS and rules of their description has been developed. By development of logic model we started with following positions.
1. The digital topographical basis represents digital model of terrain which stores the information on location, metric parameters and topological mutual relations of spatial objects, and also their semantic characteristics;
2. Digital maps and plans carry the information about the same objects with a different degree of a detail. It defines an opportunity and necessity of use uniform structure, dictionaries and libraries, including qualifier of objects;
3. The universal structure of DTMPC data includes a standard set of thematic layers with a standard set of attributes for all scale range. The database structure reflects accepted for topographical maps and plans division of objects into thematic groupings which are observed also in headings of the qualifier;
4. Terrain object coding comes true on the uniform qualifier basis. The object description in it is transferred by 8-unit codes. The same terrain object on different scale maps will differ with presence and number of specific attributes which are consolidated in classification code corresponding positions;
5. Topographic data storage with the certain level of spatial and thematic generalization is better for carrying out as uniform file in the form of seamless maps, instead of on nomenclature sheets;
6. DTCP is expedient to create and support in a compact vectorial format of data, it is preferable in the open formats accepted by the international standards;
7. DTCPs are necessarily accompanied by metadata which will allow to keep and build in the information on existence of these data on created state and world information servers;
8. Physically the structure of data is supported by the uniform model described in UML notation, patterns of geodata bases which are realized in a format of ArcGIS geodata bases and an exchange format of XML document .
The offered approach allows providing unequivocal representation, processing and interpretation of terrain objects at different levels of spatial generalization, that, in turn, creates a basis for correct overlapping the data received from different sources. The model is intended for realization in relational database and approved on maps of different scales.