Vector Data Classes
Vectors are geographic features that are represented by storing graphical information as vertex locations that are connected by lines, or in the case of points, as a symbol centered on the location. The advantage of vector graphics is that they don't
become pixelated as you zoom in and out. The major categories are Points, Lines and Polygons. The simplest data format that is used for these types of geographic elements is called the shapefile. This is a public format that was originally
pioneered by ESRI, but has subsequently released as an open standard. The Shapefile does not have any topologic information, that is information about the relationships between different elements. Shapes in a shapefile are distinguished as different
file types for Point, MultiPoint, Line and Polygon. Each shape can be paired with a row of ancillary information, called attributes, from a dbf file. The ancillary information is organized like a database table, with specific fields or columns
of information that contain values that have the same meaning and data type. The combination of a shape (or geometry) with a row of attributes is called a Feature.
The basic data access member is the FeatureSet. It has a collection of Features. Each feature has a “BasicGeometry” property and a “DataRow” property to access the vector and attribute information. The DataRows are
also stored in a table, which is in the DataTable property of the FeatureSet. More information about what a Geometry is can be found under the documentation for the Topology module. Under development are more advanced classes like FeatureRow and
FeatureTable. A FeatureRow is organized with the well known binary stored in one of the fields as a “BLOB” or “binary large object”. This binary can be translated into geometric features with the help of the WKBFeatureReader
class, but the FeatureRow hosts external properties for the Shape or Geometry to perform this translation for you and cache the result so that you don’t perform a lot of unnecessary translation.
The following tables contain information about loading times for various sizes of shapefiles.
||Size of shp
||Size of shx
||Size of dbf
||Number of Shapes in the file
||Time to Load and Display File
|| 8 MB
|| 97 MB
|Great Britain Roads
|| 6.8 Million
||1 Minute 47 Seconds
Times were calculated using the included DemoMap application.
Processor: Intel i7-3770 CPU 3.40 GHz
Ram: 8 GB
Vector Data Classes And Sample Code