The <center> element has the following definition:

<!ELEMENT center (geoFeature) >
<!ATTLIST center
  size CDATA #REQUIRED
>

The <center> element is used to specify the center of a resulting map. It has a required attribute named size, which specifies the vertical span of the map in terms of the original data unit. For example, if the user's data is in decimal degrees, the size attribute specifies the number of decimal degrees in latitude. If the user's data is projected with meter as its unit, MapViewer interprets the size in meters.

The center itself must embed a <geoFeature> element, which is specified in geoFeature Element.