To graph a functuion, one needs as much as 1 more than the number of independent variable dimensions. To graph f(x) = 3x + 1, you need a rectangular plane with x and y axis (2 dimensions). If you have a function of x and y, you need an rectangular plane with 3 axis, each orthogonal to other two.
To graph rhe domain of a function, one needs dimensions as much as the number of independent variables. Actually, we need axises for each indepentent variables; x, y, z… If we are to graph the domain of f(x, y), we are to graph something in x and y, so here is two dimensions. Domain of f(x) can be represented as a sayı doğrusu