The oldest company in (almost) every country that is still in business today was recently published by Business Financing UK in this interest.
The oldest company on the list, Kongō Gumi in Japan, has been operating since 578 AD! You can see the full resolution map here, as well as close-up maps of regions around the globe below.
As for the methodology, Business Financing says:
To create these maps, we started by reviewing various sources on the internet to locate the oldest company in each country. Once we had a list of business for each country we began researching each individual company to discover if they are still operational. If we were unsure about a company or could not discern if it was still open, we did not include it in the maps. We included both independent and state-run businesses in this list. This includes national mints, which produced coins for merchants and international customers as well as the state.Those countries where it wasn’t possible to identify the oldest business have been greyed-out on the map. Additionally, some countries have changed names or didn‘t exist at the time the oldest company opened. In all cases we have used the current country names.We created broad industry categorisations that grouped similar businesses together. Every step has been taken to ensure that the information contained within our research is as accurate as possible. However, it is possible that there are businesses still operating that predate the ones listed here. View the full-size version of this infographic.
In Southeast Asia, Pos Malaysia is the oldest company still in existence, followed by weapon manufacturer PT PINDAD (Indonesia)