The book falls naturally into two parts. Part I is concerned with the general theory of fractals and their geometry. Firstly, various notions of dimension and methods for their calculation are introduced. Then geometrical properties of fractals are investigated in much the same way as one might study the geometry of classical ﬁgures such as circles or ellipses: locally a circle may be approximated by a line segment, the projection or ‘shadow’ of a circle is generally an ellipse, a circle typically intersects a straight line segment in two points (if at all), and so on. There are fractal analogues of such properties, usually with dimension playing a key role. Thus we consider, for example, the local form of fractals, and projections and intersections of fractals.
What's the meaning of the bold text? How does one approximate a circle with a line segment? I've searched a little for it but didn't have success.