Underground Master Plan is no new for Helsinkí. Since 2011 Helsinki has been the only city in the world with an underground master plan.Plan for 2021 takes it deeper with underground business streets, underground walkways, underground maintenance tunnels going from one core of the city to another corner and in which you can ride vehicles.

This is similar to zoning plans overground that most cities in the world. Only this time, it is for underground. Helsinki's Underground Master Plan 2011 was world premiere and 2021 plan is still unique in the world. Helsinki's underground master plan is zoning for underground whereby some projects are more solid and for others not. What is important is that even for those which are not solid, a space is reserved for them, albeit roughly. Therefore when solid plans move into action, you know that planners have also considered the use of space for less-solid plans of the future. Even the non-planned but likely projects are marked in this plan. In plain English, Helsinki City does what urban planners had been doing for years for the overland cities.

Helsinki Underground Master Plan is naturally a living plan. For example, the 2021 plan removes some of the zoning, space allocations which were made in 2011 plan and adds new ones. Things have moved on since 2011. Technology has developed. New tunnel technologies, new infrastructure technologies, new transport technologies emerged.

Helsinki City describes the Underground Master Plan as such:

For Helsinki, a new underground master plan is being prepared, which controls the planning of spaces and tunnels in the Helsinki bedrock.
The current plan, which came into force in 2011, should be renewed because some of the underground reserves specified in it are outdated, while new needs have arisen.

Helsinki's new general plan makes the city denser and growth is generating pressure to move various underground functions underground and utilize underground premises more efficiently than hitherto. The new underground master plan aims to increase the versatile use of premises underground, improve the systematic use of rock spaces and coordinate different types of functions.
The underground master plan only includes the most important underground projects. Underground projects can also be implemented based on detailed plans.

Timetable for the preparation of the plan
The preparation of the new underground master plan was initiated in 2017. The draft plan is expected to be considered by the Urban Environment Committee in early 2020. Based on the draft, a draft plan is prepared, which the board is expected to decide on by the end of 2020. The city council makes the final decision on the plan.

The public Underground Master Plan 2021 can be reached from this page below. Sorry I have access to only Finnish language plans. Please click on the Materialen till Helsingfors nya underjordiska generalplan at the bottom of that coming page to see the detailed plans.

https://www.hel.fi/helsinki/sv/boende-och-miljo/planlaggning/aktuella/underjordiska-generalplan

Note: There were many interesting photographs in Helsinki City's detailed plans. I chose not to use them thinking that Helsinki City probably licensed them from photography artists and copyright rights are not transitive. Helsinki City paid the artists but it does not entitle me to use it. Therefore I chose to use photograph of Underground City (Montreal Canada)  from Wikimedia Commons. I want to thank 'Laslovarga' for making this photograph available to public.