Henri Lefebvre, in his book The Production of Space, defines three spatial concepts, being mental, social and physical spaces. Lefebvre holds that mental, social and physical space, are in fact indivisibly linked, because each one has inherited implications from the others. We cannot talk about a pure mental space that is not contaminated with social relations and physical perceptions; in the same way, the mental space is where we will conceive and analyse social events and physical surroundings; the physical space, in its turn, can be approached, in the end, as a consequence of mental and social spaces.
The concept of space as a pure empty or even a natural reality is, according to Lefebvre, simply a representation. This representation occurs in our mental space, our cognitive powers, imagination etc. To imagine this mental space as a blank piece of paper on which we write our cultural history is also a misconception. Our mental space is already filled with history, by means of culture, brought by past experiences, by previous knowledge and beliefs; in reality, all the transformations that society undergoes.
As a Marxist, space for Lefebvre is always about production which also makes it political, particularly urban spaces of the western industrialized world. Lefebvre believed it is so governed by abstraction that even the sensory and practical aspects of human life are represented and communicated primarily in terms of quantities, commodities, and categories.
What is an ideology without a space to which it refers, a space which it describes, whose vocabulary and links it makes use of, and whose code it embodies? (…) What we call ideology only achieves consistency by intervening in social space and in its production, and by thus taking on body therein (Lefebvre).
Furthermore, Lefebvre writes that experts, such as urbanists, planners and scientists, tend to assert an official representation of social space as the one true space, a central reference point of knowledge, government, and professional authority. They privilege the element of ‘conceived space’ and repress the element of ‘lived space’, thereby forcefully producing homogenous built and social environments. Lefebvre coined this the monotony of everyday life. A homogenised, commodified, rationalisation of all the spheres of life.
Lefebvre was concerned with the power relations embedded in space. In opposition to the expert representations of true space, are representations of the “truth of space” which include diverse, even divergent sociospatial processes that are not authorized by the dominant culture. Within our urban spaces opposition and new representations appear in the form of street art, grafitti, vandalism, protest rallys and street marches.

“I want to be a non conformist” graffiti poster. source