You may make the graphic characteristics of your objects change in response to a change in a user variable. For instance, if your map objects represent real world objects that did not exist before a certain date, you may place that date in an attribute field and create a graphic characteristics specification that sets the object's visibility to "Hidden" if the user variable is set to a value which precedes that date. This way you can set the user variable to a specific date, and the map will be redrawn as appropriate for that date. (If you don't know how to add attribute fields or create graphic characteristics specifications, see Edit Attribute Fields or Edit Graphic Characteristics.)

For example, consider a map that shows railway lines. Each line object has two attribute fields: "start" and "finish". In the "start" field is placed the date on which construction began, and in the "finish" fields is placed the date when construction was completed. For displaying this map, three graphic characteristics specifications are used. The first has a selection rule of "$all", and sets all lines to a width of 3 and the color red (just because we like fat, red lines). The second has a selection rule of "finish > $var" and sets a dash style for those lines -- thus all lines that had not been finished by the date in the user variable will be dashed. The last has a Selection rule of "start > $var and sets the visibility to "Hidden" -- thus any lines which had not been started by the date in the user variable won't be seen at all.

To set the user variable, choose Variables from the Edit menu.

The Edit Variables window opens. (The name is anticipating multiple variables in future versions; this version of XViewSDTS supports only one variable.) Any numeric value may be entered into the Value box.


Point to the Value box and use the Backspace key to clear the current value. Then type in your desired value.

In this example, the date of January 1, 1846 is entered (using the YYYYMMDD format of date fields).


If you want to step through the years, point to the right of the year and click to move the text caret. (Alternatively, you may point anywhere in the Value box and move the caret with your keyboard's cursor keys.)


The caret is now to the immediate right of the year digits. Now when you click the + button, the year will be incremented.


Clicking the + button increments the year to 1847.


The map now shows railroads completed and under construction on January 1, 1847.


Clicking the + button again increments the year to 1848.


The map is redrawn and shows that some railroads were completed during 1847, so are now displayed as solid lines, while construction has begun on other railroads, which appear as new dotted lines.


Clicking the + button again brings us to January 1, 1849.


The railroad network continues to expand.


You may leave this window up to keep it handy, or you may click Close when done with it.

Copyright © 2005 by Dapper Mapper