To specify the location of DITA DTD files:
[Setup]
; DTDPath = path to location of DITA DTDs, default none
DTDPath=D:\path\to\DTDs
The OASIS DITA 1.1 DTD is in directory %omsyshome%\d2g\dtd of your DITA2Go installation.
You can override the setting for DTDPath with the -d switch on the dita2map.exe command line; see §46.4 Running DITA2Map.
If you run DITA2Map without specifying a value for DTDPath, either in a configuration file or with the -d switch, DITA2Map will try to read the DTD referenced in the SYSTEM ID, normally the one at OASIS, and most likely will fail. That is, DITA2Map will write an empty map with no topicrefs, just header and ending.