From the figures describing land use in France (source IFEN), I calculated the total surface covered by buildings, roads, and artificial surfaces not built (typically gardens). I also calculated the rate of increase of these various surfaces (below, surfaces are in square km).

Année	1992	% of total	1993	% of total	1994	% of total	1995	% of total	1996	% of total	1997	% of total	Change from 1992 to 1997	By year
Artificialized land not built	13 236	2,42%	13 534	2,47%	13 936	2,54%	14 232	2,60%	14 553	2,66%	14 798	2,70%	+11,80%	+2,26%
Built land	9 424	1,72%	9 589	1,75%	9 736	1,78%	9 848	1,80%	9 955	1,82%	10 077	1,84%	+6,93%	+1,35%
Roads & parking lots	15 354	2,80%	1 5572	2,84%	15 798	2,88%	16 006	2,92%	16 246	2,96%	16 346	2,98%	+6,46%	+1,26%
Forests	144 221	26,32%	145 920	26,63%	147 211	26,86%	148 097	27,03%	148 871	27,17%	149 292	27,25%	+3,52%	+0,69%
Anual cultures	151 558	27,66%	151 990	27,74%	151 617	27,67%	151 413	27,63%	152 202	27,78%	153 115	27,94%	+1,03%	+0,20%
Rocks and water	18 373	3,35%	18 308	3,34%	18 375	3,35%	18 373	3,35%	18 393	3,36%	18 416	3,36%	+0,23%	+0,05%
Permanent cultures (fruit trees...)	13 193	2,41%	13 189	2,41%	13 080	2,39%	13 016	2,38%	12 899	2,36%	12 853	2,35%	-2,58%	-0,52%
Grasslands	116 888	21,33%	115 105	21,01%	114 107	20,82%	113 766	20,76%	112 524	20,54%	111 267	20,31%	-4,81%	-0,98%
Mountain pastures	45 038	8,22%	44 449	8,11%	44 068	8,04%	43 409	7,92%	42 951	7,84%	42 516	7,76%	-5,60%	-1,15%
Scattered trees	20 669	3,77%	20 313	3,71%	20 046	3,66%	19 810	3,62%	19 359	3,53%	19 271	3,52%	-6,76%	-1,39%
TOTAL	547 954		547 969		547 974		547 970		547 953		547 951
Of which artificialized	38 014	6,94%	38 695	7,06%	39 470	7,20%	40 086	7,32%	40 754	7,44%	41 221	7,52%	+8,44%	+1,63%

All this fits what we know : urbanized land and forests grow, while grasslands decrease. One of the driving forces of this evolution is something called peri-urbanization, which designates the process by which cities grow by increasing their suburbs.

France in 1936 : 41,5 millions inhabitants	France in 1999 : 58,5 millions inhabitants (+40%). Some urban areas have grown tenfold, while rural areas emptied.
> 1000 hab/km2 500 à 1000 hab/km2 200 à 500 hab/km2 100 à 200 hab/km2 70 à 100 hab/km2 50 à 70 hab/km2 30 à 50 hab/km2 < 30 hab/km2

One might then ask oneself the following question : if we prolongate the present trends for converting "natural" land to "artifical" land, how long does it take to have cities and roads covering 100% of the mainland France ?

If we do that exercise, that is calculating the portion of the mainland covered by cities, roads, etc, by prolongating the average anual increase for the period 1992 - 1997 (that is 1,63% per year), we get the following curve :

Fraction of the mainland urbanized depending on the number of years after 1998.

We see above that a prolongation of the present growth rate means that mainland France has been turned to a single city in 160 years. If we assume that we cannot do without a fat 50% for agriculture and forests, then it just takes a century to urbanize the remaining 50%.

Is it legitimate to assume a growth constant in percentage and not in absolute figures ? (which would mean so many hectares per year). We must remember that a growth expressed in percentage corresponds to the case when the yearly increase is proportional to the existing value. If the increase results from peri-urbanization, assuming that the increase (at the border of the cities) is proportionnal to the size of the city is not totally stupid.

Still, the above calculation has no predictive value, of course ! In particular, when there is an upper limit to something (which is the case here : it is not possible to go over 100% of the mainland !), the general evolution never resembles the above curve, but has rather a "S-shaped" aspect, like the curve below.

General aspect of processes starting from zero and limited by an upper value (the horizontal axis represents time).

This being said, this little calcculation gives a rough idea of the speed at which we are currently modifying land use in France, and underlines the fact that this is absolutely not "sustainable". To be "sustainable" an evolution must not meet its limit before a century !

Let's recall that land is a limited (and not renewable !) resource, even if we can change land-use.