var zo=1;

function zoom()
{

if (zo==1)
{
zo=0;
document.getElementById('img_plan').style.width = '90%';
document.getElementById('legende').style.display = 'none';
document.getElementById('boutton').value = 'zoom -';
}
else 
{
zo=1;
document.getElementById('img_plan').style.width = '52%';
document.getElementById('legende').style.display = 'block';
document.getElementById('boutton').value = 'zoom +';

}}