How to create tilemaps from individual png

First download shoebox from:

http://wdbase.de/download/tools/shoebox.html

Then download gimp's David's Batch Processor from:

http://members.ozemail.com.au/~hodsond/dbp.html

Use the Batch Processor to resize the individual tiles to 32 x  32.

Then use shoebox to create the tilemap.

Follow the instructions here on how to use shoebox:

https://www.scirra.com/tutorials/1046/create-a-tilemap-with-the-mapeditor

Start ShoeBox and perform a right mouse click on "Sprite Sheet" (First Tab) to enter settings. Now choose the "Default" method and change this two values.

Tex Crop Alpha to false
Tex Exdrude Size to 0
Tex Padding to 0

And save your option by clicking "Apply". Now go to your folder with the separated files and drag them into the "Sprite Sheet" tab at ShoeBox.