I've run into this as well...our map should default to one of several sites, but no amount of fooling with the fitExtent and extent parameters (including shrinking the default extent) produces a sure fit for all of them. More often, the map starts up one level too far in for some, or one level too far out for others. And there's also cases where the map should start up where the user previously left off, and even with the same screen size as before, the map still often starts at the wrong zoom level. It's been giving me fits for awhile, but I've gotten to the bottom of it.
The reason this occurs is found in the _coremap module. In the _addLayerHandler function, observe what happens when the map's graphics container is added (when the map loads):
if (a === this.graphics) {
...
this._firstLayerId = null;
...
d = this._fixExtent(b, i.fitExtent);
this.extent = d.extent; //THIS LINE CAUSES THE PROBLEM
this.__LOD = d.lod;
this.__setExtent(this.extent, null, null, i.fitExtent);
...
}Notice the call to __setExtent. One of the first things that happens in __setExtent is another call to _fixExtent - with the already-fixed extent. This extra call can result in an expanded extent that causes the map to start up one zoom level out from where it should.
The simplest fix is to rewrite the problem line to:
this.extent = this.extent || d.extent;
If you have a local copy of the API, you can implement this fix on your own, but that can be tricky. You'd have to update init.js, and finding that particular line can be difficult, especially since variable names can be different.
There are workarounds though. I've written a function called setDefaultExtentOptions that adjusts your default extent to match the actual extent your map will show, and appends appropriate values to the options parameter (the second parameter) that you pass into the map's constructor.
The function and workflow would go like:
function setDefaultExtentOptions(defaultExtent, mapContainerID, options) {
var contentBox = domGeom.getContentBox(document.getElementById(mapContainerID));
var extentHeight = defaultExtent.getHeight();
var extentWidth = defaultExtent.getWidth();
var viewHeight, viewWidth;
var lods = options.lods;
var dY, dX;
var center;
var lod;
options.spatialReference = defaultExtent.spatialReference;
options.extent = defaultExtent;
options.fitExtent = true;
for (var x = lods.length - 1; x >= 0; x--) {
lod = lods;
viewHeight = lod.resolution * contentBox.h;
viewWidth = lod.resolution * contentBox.w;
if ((viewHeight > extentHeight) && (viewWidth > extentWidth)) {
center = defaultExtent.getCenter();
dY = viewHeight * 0.5;
dX = viewWidth * 0.5;
options.extent = new Extent(center.x - dX, center.y - dY, center.x + dX, center.y + dY, defaultExtent.spatialReference);
options.fitExtent = false;
options.scale = lod.scale;
options.zoom = lod.level;
options.center = center;
return;
}
}
}
var defaultExtent = new Extent(minX, minY, maxX, maxY, new SpatialReference(wkid));
var divId = "map"; //set according to your div's ID.
var options = {
//set map options here...MUST INLCUDE VALUE FOR lods
};
setDefaultExtentOptions(defaultExtent, divId, options);
var map = new Map(divId, options);I implemented this workaround before actually figuring the problem out. There are probably better workarounds, but optimally, a workaround wouldn't be necessary.
I see the question was initially raised for 2.8, but it's still happening in 3.13, which I'm using.
