The MapViewer JavaScript functions for controlling navigation include the following:

• recenter(x, y) sets the center point of the current SVG map.

  The input x and y values specify the coordinates (in pixels) of the new center point, which is the point inside the SVG map to be displayed at the center of the SVG viewer window. The SVG viewer window is the graphical area in the web browser displayed by the SVG viewer. The coordinates of the center point are defined in the SVG map screen coordinate system, which starts from (0, 0) at the upper-left corner of the map and ends at (width, height) at the lower-right corner.

• setZoomRatio(zratio) sets the current map display zoom ratio.

  This function can be used to zoom in or zoom out in the SVG map. (It does not change the center point of the map.) The original map zoom ratio without any zooming is 1, and higher zoom ratio values show the SVG map zoomed in. The map zoom ratio should be set to those values that fit predefined zoom levels. For example, if the zoomlevels value is 4 and zoomfactor value is 2, map zoom ratios at zoom level 0, 1, 2, and 3 will be 1, 2, 4, and 8, respectively; thus, in this example the zratio parameter value should be 1, 2, 4, or 8. For more information about predefined zoom levels, see the descriptions of the zoomlevels, zoomfactor, and zoomratio attributes in map_request Attributes.