This tool offers an easy to use method to fit a custom shape to the grid. It can be used to resize arbitrary shapes, but it's core use is focussed on maps.
To use the map tool, a shape first needs to be selected. If this is not the case the map tool will inform you of this and you'll be able to select a shape from within the map tool without switching to the select tool.
If a shape is selected, you'll be able to select a region in this shape that you want to use as a reference. For example selecting an area that should represent a 3 by 3 area on the grid. You can resize and further tweak this selection after your initial selection to make sure it covers exactly what you desire.
If the selection is adequate you can insert the X and Y dimensions the selected area should occupy and press apply.The above is an example of using the map tool to refit the imported map asset to the grid. We selected an area, performed some slight modifications and then informed the tool of the desired dimensions.