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Some overlay maps allow you to make the graphic characteristics of the objects change in response to a change in a user variable.  For instance, such a map may have objects that represent real world objects that did not exist before a certain date.  That date will be included in an attribute field and the graphic characteristics file will instruct Place-n-Time to set 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.

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.

The graphic characteristics file for this map will instruct Place-n-Time to set a dash style for those lines where the "finish" attribute is greater than the user variable -- thus all lines that had not been finished by the date in the user variable will be dashed.  Similarly, the object's visibility will be set to "Hidden" for those lines where the "start" attribute is greater than the user variable -- 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 View menu.

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

Type in your desired value into the Value box.

In this example, the date of January 1, 1846 has just been typed (using the YYYYMMDD format of date fields).  The background has turned yellow to indicate that value has not yet been entered, and the map has not yet changed to reflect this date.

Press Enter to enter the date and update the map.  The background will turn white.

If you have typed a non-digit, the background will turn red when you press Enter.  Simply correct the mistake and press Enter again.

If you want to step through the years, click one of the arrow buttons under the last digit of the year.  Clicking the up arrow increments the year to 1847.

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

Clicking the up arrow 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 up arrow 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 © 2008 by Dapper Mapper

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