FOAM secures physical space on the Ethereum blockchain which is a World Computer and database that stores information across a peer to peer network without a single point of failure or the need for any administrators. This enables a decentralized map that is completely controlled by the community. Transactions are how computation and storage are performed on the Ethereum blockchain.
Interactions besides viewing the FOAM Map require transactions to be submitted to the Ethereum blockchain. This is where Gas comes in.
Gas is the metering unit for use of Ethereum World Computer. Additional computation and storage uses more gas. You can think of it like the gallons of fuel you need to power a car.
By metering the usage, people (called miners) who operate the World Computer can be compensated and are incentivized to participate.
Miners are paid a fee for processing transactions calculated as a percentage of the gas needed for that transaction.
The gas and the fee are not the same thing, and the fee miners are paid is based on the amount of gas used.
The FOAM Map uses Ethereum for computation and storage every time you add or challenge a POI, participate in a vote, or change the status of a POI.