The Next Earth Project uses blockchain technology to handle payments and store the ownership of Lands. The chosen blockchain technology is the Polygon Blockchain because of its advantages over Ethereum (like low gas fees and fast block times), allowing for the best available user experience. The two main parts of the smart contract architecture are the Payment Contract and the NFT Contract.
All LAND bought on Next Earth is represented on the blockchain by an NFT (Non Fungible Token). It’s a special smart contract based on the ERC721 token standard, which ensures the immutable proof of ownership and holds the base data of the LAND, like the hash of the unique identifiers of the tiles that the LAND contains. Because all tiles have a unique ID on the map, which clearly defines its position, the NFT ensures that the owner of the NFT owns the LAND and owns all tiles on the map that contains the LAND. Besides that, the token includes the availability of the LAND’s metadata which holds more detailed information about the NFT.
The ERC721 standard structure of the smart contract contributes to the future integration of third party marketplaces or any other dApp that handles standard NFTs, as well as taking advantage of the blockchain technology NFT ecosystem.
All payments for purchases and trade of Lands in The Next Earth Project go through the Payment Contract, a specially designed contract written in Solidity.
It handles the payment allocation in a secure, trust-less, and fully transparent way. All transactions will be recorded on the blockchain and anyone can check them. During the design of this contract an important key is to keep the transaction’s gas fee as low as possible utilizing several smart contract design techniques.
The grid layer on the map is represented by approximately 10m x 10m rectangles (called “tiles”) calculated by the Mercator projection, which is a cylindrical map projection. It allows for the translation of the latitude and longitude based system of the Earth into a 2D map.
Every tile has a unique id which clearly determines its position on the map including the boundary box’s latitude and longitude values. This unique ID is also calculated based on the Mercator projection and on the Mapbox tile system.
All tiles are classified into three classes: Urban, Non-Urban, Water
• Urban Tile: we define urban tile as a tile which is inside a country’s border and has approximately a 1 square kilometer boundary box that has at least one POI. The POI database that we use is extracted from the OpenStreetMap dataset.
• Non-Urban Tile: every tile inside a country’s border which is not an urban tile.
• Water Tile: every tile which is not inside in a country’s border.
For the map view, we use Mapbox and the Mapbox API. The grid layer, which is the presentation layer of the tiles, also uses the Mapbox API and several features of it like GeoJSON, world coordinates, tile coordinates, and its drawing system.