IMPROVING THE CONSISTENCY BETWEEN TILES IN TILES BASED GIS - CASE STUDY: SURVEY DEPARTMENT 10K DIGITAL TOPOGRAPHICAL DATABASE

摘要

Survey department of Sri Lanka is presently creating 1 : 10,000 (10K) digital topographical database. Data are stored in Arc Info coverage format based on tiles. Each 1 : 50,000 (50K) tile is subdivided into 25 numbers of 10K tiles. There are twelve coverages in each tile depending on the availability of data and the availability of features in real world. These coverages represent point, line, polygon features or combinations of points, lines and polygons.Creation of 10K data is done by several ways. Existing 10K hardcopy maps are scanned and digitized on screen in AutoCAD platform for conversion them into Arc Info coverages. Digital cartographic model data in DGN format and field survey data collected using GPS too are converted into Arc Info coverages. Data conversion process is presently carried out based on tiles since source data are available in tiles. Due to conversion of data is done based on tiles, some inconsistencies could be observed between tiles. It will make problems when data in several tiles are to be combined and analyzed. Those inconsistencies need to be identified and measures need to be taken to avoid or minimize the inconsistencies.Existing 10K coverage data stored in tile base were studied to examine the possible types of inconsistencies between tiles. From this study, the structure of the available data, different field names and their size definitions associated with each coverage were identified. Further, how different attribute fields are organized in the attribute tables was examined. Then a method was developed to identify the availability of attribute fields, inconsistencies in field sizes and placement order of fields, automatically. Once the inconsistencies are identified, the method was then improved to correct those inconsistencies automatically as much as possible and to report the errors that can not be automatically corrected.