LTJ or Luontotietojärjestelmä is the new prototype REST and WFS API to the City of Helsinki nature information database operated by the Helsinki Environment Center.

It contains information on notable geographical and natural features and all species, species observations, habitats, protected areas and conservation programmes within the City of Helsinki, used by the Finnish Biodiversity Info Facility as well as other environmental agencies.

Some of the data is protected for conservation reasons and only available for authorities or registered users of the APIs, but all the content visible for anonymous users is open data and may be used under the CC-BY 4.0 license.