The module looks great, except that I get the following error:

Code:

Notice: Undefined variable: markers in /home/username/public_html/modules/mod_j15visitormap/mod_j15visitormap.php on line 114

Since I'm here, one question about customization: Can I make width percentage instead of pixels? If so, how? Thanks

If you get "Notice: Undefined variable:" this means that your PHP installation is configured to show both Errors, Warnings and Notices.
You should configure your PHP installation to only show Errors and Warnings which is the default PHP installation.

This is done by editting your php.ini file.
Open your php.ini and locate the error_reporting setting. Edit this line to be as follows:
error_reporting(E_ALL ^ E_NOTICE);

Also, the percentage should work for the width.