You can click on the link in the description for the interactive map. Portugal comes from the line

ਯਰਮਨ ਪੁਰਤਕਾਲ ਮਲਾਈ ਬੁਕਸਰ ਖਿੰਗ ਅਰੁ ਖਿੰਗਈ ॥

ਯਰਮਨ (yarman) is Germany, ਪੁਰਤਕਾਲ (purtkal) is Portugal, and ਮਲਾਈ (malei) is Malay. The line comes from Sarbloh Granth which is written in Braj and is not translated into English yet unfortunately.

I don’t know Braj well, so take my explanation of why Portugal is mentioned in this line with a grain of salt: Sarbloh Granth is a classical Indian epic poem about gods fighting demons. In this line the poet says the defeated demons’ descendants still live across the world, and he names real foreign places his readers knew of, such as Germany, Portugal, and the Malay Peninsula. Guru Gobind Singh (traditionally attributed poet) criticized people who recited the epics and worshiped warrior deities but wouldn’t stand up to oppression themselves. I interpret this line as him merging mythology with real-life, reminding the reader that the “demons”/oppressors still live in all corners of the world today. This inspires his followers to do the “real” worship of their gods and goddesses, which is to emulate their fight against oppression rather than just doing empty rituals while their neighbors are being pillaged.

There are other European places like Poland mentioned in Dasam Granth, which is mostly translated line-by-line into English. You can click the link to SikhiToTheMax and read in English around that line to understand the context.