これは私がこれを行うために使用したコードの例です。マップの最初の範囲を設定して米国を表示する場合、これはあなたのケースでうまくいきます:
//This function limits the extent of the map to prevent users from scrolling
//far away from the initial extent.
function limitMapExtent(map) {
var initialExtent = map.extent;
map.on('extent-change', function(event) {
//If the map has moved to the point where it's center is
//outside the initial boundaries, then move it back to the
//edge where it moved out
var currentCenter = map.extent.getCenter();
if (!initialExtent.contains(currentCenter) &&
event.delta.x !== 0 && event.delta.y !== 0) {
var newCenter = map.extent.getCenter();
//check each side of the initial extent and if the
//current center is outside that extent,
//set the new center to be on the edge that it went out on
if (currentCenter.x < initialExtent.xmin) {
newCenter.x = initialExtent.xmin;
}
if (currentCenter.x > initialExtent.xmax) {
newCenter.x = initialExtent.xmax;
}
if (currentCenter.y < initialExtent.ymin) {
newCenter.y = initialExtent.ymin;
}
if (currentCenter.y > initialExtent.ymax) {
newCenter.y = initialExtent.ymax;
}
map.centerAt(newCenter);
}
});
}
これが動作するjsFiddleの例です:http://jsfiddle.net/sirhcybe/aL1p24xy/