Summary: Structure of spatial data in ILWIS
In this section you learned the following:
- ILWIS uses two types of maps: vector maps and raster maps.
- Vector maps in ILWIS are either point maps, segment maps or polygon maps.
- Vector maps can be obtained either by digitizing analog maps, or by importing
them from other sources.
- Raster maps can be obtained either by rasterizing vector maps, by importing them
from other sources or by performing GIS or image processing operations in ILWIS.
- Raster maps, polygon maps, segment maps, point maps, tables and columns are
called data objects. They contain the actual data.
- Service objects are used by data objects; they contain accessories that data objects
need besides the data itself. Domains, representations, coordinate systems and georeferences
are called service objects.
- Vector maps need a number of service objects: a domain, a representation and a
coordinate system.
- Raster maps also need these service objects: a domain, a representation and a coordinate
system. All raster maps contain information in discrete cells or pixels, which
are ordered in rows and columns. To relate these pixels to map coordinates another
service object called a georeference is needed.