File of SHP format is a binary file which contains graphic data (shapes; this notion is analogous to the ObjectLand notion of feature). All shapes of one SHP file have one and the same spatial category which is called “shape type”. It is indicated in the header part of the file.
A set of shape types of SHP file differs from the set of ObjectLand spatial categories considerably, it includes the following types:
Point – corresponds to ObjectLand point feature;
Multipoint – a set of points which is processed during import as several separate point features;
PolyLine – a composite line shape which in fact can consist of several polylines, in this case it is imported as several separate line features of ObjectLand;
Polygon – a composite area shape which in fact can consist of several polygons (possibly containing holes), in this case it is imported as several separate area features of ObjectLand;
PointM, MultiPointM, PolyLineM, PolygonM – “measured” shape types which differ in the fact that for every point specified, apart from its coordinate X and Y, real number M called “measure” of this point is given. When importing to ObjectLand this measure is ignored and “measured” forms are imported as usual ones;
PointZ, MultiPointZ, PolyLineZ, PolygoneZ – a set of 3D shape types in which apart from values X, Y and M coordinate Z is indicated for every point specified. When importing to ObjectLand Z coordinate and the measure are ignored, three-dimensional forms are imported as the corresponding usual ones;
MultiPatch – shapes which describe composite three-dimensional areas, when importing to ObjectLand they are considered as area features;
Null Shape – a fictitious shape to which no graphics corresponds, but with which some attributive data can be linked.
To store attributive data linked with shapes of SHP file the file with DBF extension with the same name is used which corresponds to the widespread dBASE format. A record of DBF file the number of which corresponds to the sequence number of this shape in the file corresponds to every shape of SHP file. When importing from SHP format attributive data from DBF file is loaded to the table linked with corresponding feature type of ObjectLand map. If the shape of SHP file is imported as several ObjectLand features, every feature is linked with one and the same table record.
The file used for storing field values of the type “memo”, that is, strings length of which can differ for various records, can be used as addition to DBF file. Since there are no limitations on length of fields in ObjectLand, memo fields can be imported to string fields of GDB tables. Name extension for the file of memo fields depends on selected variant of dBASE format.
The presence of DBF file is not the necessary condition for importing features from SHP file to ObjectLand map. If there is no DBF file, no table records will be linked with features being imported.
Import of data of DBASE format is described in more detail in chapter 69 “Import of table data of dBASE format”.
For every shape of SHP file the file with SHX extension contains offset of the description of this shape from the beginning of the file. SHX file data permits speeding up search of features by its number considerably. When performing import to ObjectLand, data of SHX file is not used and the presence of such a file is not required.
Detailed description of format of SHP files is given in documentation on software products of ESRI, Inc.
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