contents.gifindex.gifprev1.gifnext1.gif

Importing ASCII "route" features

A "route" data set is created from one ASCII file, but consists of two data set members: a point theme and a line theme. The point theme includes the location of points along the "route", e.g. a ship route or historical voyage, and has attribute values describing some aspects of each point along a route. The line theme is created as lines through each set of point co-ordinates and with attributes describing some aspects valid for each route feature.

The procedure for importing "route" features is fairly similar to the general procedure for importing spatial ASCII data, but as two themes are created, the specified filename is used as basename, where the point theme name is extended with _p, and the line theme name with _l. In this way the two themes are stored in different shapefiles (which they must be), but it is easy to identify the two shapefiles making up a "route" feature.

Another difference is that when specifying the output shape file name in Step 5, you cannot use more than 6 characters (before the .shp extension) for the filename. The reason is that these 6 characters are used as basename, where the point theme is extended with _p, and the line theme with _l. In this way the two themes are stored in different shapefiles (which they must be), but it is easy to identify the two shapefiles making up a "route" feature.

After the "route" shapefiles are created they are added to the view as new themes. The point theme is given a name consisting of the basename + "Waypoints", while the line theme is given a name consisting of the basename + "Route". The table shows how the user's choice of shapefile name is utilised.

Example of naming conventions for "route" features:

User's shapefile name Feature type Actual shapefile names Theme names

sail95.shp point sail95_p.shp sail95 Waypoints

line sail95_l.shp sail95 Route

To import route features from an ASCII file, choose the New Theme from ASCII file menu choice in the View menu in the view window.