Mayor Anne Hidalgo thinks it’s time to tear up the historic map of Paris and start again. This could get tricky.

It’s time to tear up the historic map of Paris and start over. So suggests a new proposal from Paris Mayor Anne Hidalgo, leaked from a “confidential note” to France’s President and Prime Minister last week. According to the note, Paris needs its internal boundaries redrawn so that its arrondissements—Paris’s equivalent to boroughs, albeit generally far smaller than their U.S. equivalents—are closer to each other in population size.

There’s some sense in the proposal, but it would be a major shake-up nonetheless, not least a psychological one for Parisians. The city’s arrondissement boundaries have changed very little for over 150 years, their spiral layout and numbers being central aspects of how Parisians describe and navigate their city. Rubbing these boundaries out, say critics, would put Paris “at risk of losing its identity.”

The case for redrawing the boundaries is strong. When they were first drawn up in 1860, the arrondissements divided a Paris radically different from today. The city core teemed with residents packed tightly together, while the outer areas were either less developed or still un-built. At the time, it made perfect sense to have smaller boroughs in the center and far larger ones on the periphery.

Accordingly, the city drew up the characteristic snail shell spiral map of arrondissements, the first to fourth forming a tight little central loop around which the others coil steadily outwards. For outsiders, this can be a little confusing. For example, you might expect the 16th and 19th arrondissements to be nearer to each other than they are to the 1st, but instead they’re on either side of the city, with the 1st sandwiched in the middle. Still, it’s something most people can get the hang of fairly quickly.

What’s harder to grapple with is just how much Paris has changed since the boundaries were drawn.