It's easy:
1. Login to your server on any character.
2. Put server files:
data/items/items.otb
data/world/(all files)
In folder
data of OTClient. It will look like this:
Then in OTClient open Terminal (CTRL+T) and type:
PHP:
g_things.loadOtb('items.otb')
Then (replace 'ots' with your map name):
PHP:
g_map.loadOtbm('ots.otbm')
It will freez OTClient for few seconds.
DONE!
You got full OTS map on minimap. After relog, it will save that map in OTClient config directory
.otclient.