Cards have 0-3 tags that thematically describe them and allow other cards to relate to them. There are no special rules for the different tags. The icons below are listed from left to right on the upper picture.
City: This project places a city tile. This often requires energy production and produces M€.
Event: This project is a one-time event. All events are red cards that are turned face down after being played.
Earth: This project is related to activities on Earth.
Plant: This project involves plant life or other photosynthesizing organisms.
Space: This project uses space technology. Titanium may be used to pay for this card.
Jovian: Means 'having to do with Jupiter'. This project represents infrastructure in the outer solar system.
Science: This project enhances your scientific knowledge. Some cards require science tags.
Building: This project involves construction on Mars. Steel may be used to pay for this card.
Power: This project is focused on energy production or handling.
Microbe: This project involves microbes for specific purposes.
Animal: This project involves animals. Generates VPs.