The world map is a model of the Earth, it tries to solve a specific problem of planning shipping routes. As you can see Greenland is much much bigger than it is in reality, but this is because the purpose of the map is to find angles to sail, not to display the relative sizes of parts of the world. This is the most important concept
for DDD because when we write software (using OOP in particular, more on this later) we are
actually solving a problem by creating a model (since OOP based upon
concepts and 'real things')
In software we aim to create highly modular programs. We do this because it makes the software easier to create and maintain since we only have to think about a small set of things at a time.
Using the OOP paradigm, objects are supposed replicate real-life things (as Bertrand Meyer puts) as a "cousin twice removed" from reality. So, to modularize our OOP programs into simplified models provides a perfect match.
- OOP for modelling concepts as objects.
- Models made from objects for solving a problem.
- Models divided into contexts to modularize our software.
Here is the talk Eric gives that explains it: https://youtu.be/pMuiVlnGqjk?t=1789
It's very difficult to summarise such a large topic but here are some links that explain the concepts.