Moving relatively small map area like BW town might be done simply by selecting the town area and saving it as object.x
But if map editor collapses when saving that object.x, then you need to split the selection to two or more parts, each saved separately as object.x
Map editor is a 32 bit program and can only use a limited amount of memory (whereas 64 bit program can use all of your computer RAM), so when the memory overflows because you selected too big a map chunk for saving, the program closes on you.
The editor has most memory available to use when it is freshly started, before it gets fragmented as you do other things in it. So when copying (grasping) the whole town, do it in newly opened editor instance. Then if it still fails on few tries, copy smaller sections and join them on new map canvas.
Grasping and placing all three layers 'Ctrl-6' is best done when you display big tile grid 'G' and also display coordinate readout 'Ins'.
Start dragging the selection rectangle from a tile that has both x/y coordinates even number (in top left quadrant of one of the big tile grid) and end the selection on both odd coordinates tile (bottom right quadrant of the big tile.
Then click '5' to show grasped object at mouse tip ready to place on map.
Now you need to experiment on which tile to click (both odd or both even or mixed even/odd) to place the object where you want it to be placed.
If the coordinates under your mouse cursor are mixed, even and odd or both odd, the object gets placed on tile over to one side, horizontally or vertically. Its been a while since I played with this and you need to experiment to get hang of it.
To have control over the result, you need in the first place to have drawn the grasping selection rectangle to fully include big tiles in it, that's why the selection needs to follow the big tile grid outlines (G). That is, it needs to start on both even coords and end on both odd coords.
The reason for this weird behavior is the back tiles are made up of four small tiles (their single tag is in the upper left tile of the four) and so they allow placing only on every other tile, horizontally or vertically. So when placing grasped object that includes back layer big tiles, the image at the mousetip as you click to place the object on map jumps to the nearest tile it can be placed on. This can be confusing if you are not quite familiar with how things work under the hood.
I wish that the object at the mouse tip (when you click 5 and it is ready to be placed on map) would 'hang' on it down and to the right, with mouse arrow showing over the first small tile where you started drawing the grasping selection. Instead the object shows up above mouse arrow cursor and to the right and in addition you get what looks like unpredictable behavior when placing the object on map. But with little experimenting you can place it where you want it.
Mind you, when placing the whole town on a new blank map, there is no issue of this sort. Also when copying or moving all three layers together, you would rarely place it on the existing map ground tiles, so it is just as well that this stays as it is without making an effort to make it more user friendly.
This grid is big tile grid G, each rectangle encloses four small tiles.