This is based on form109's "Largest installation of mercs." But mine is on LPS. If anyone has ever seen a whole lot full of LPS lights in one place. I'll will start.

#1 - A parking lot with AEL 180w LPS fixtures. Parking lot is likely assigned so no issue of finding where you parked. Can't see the numbers since it's being repaved.

#2 - Another parking lot lit by LPS. This one is definitely assigned as I can see the numbers on the slots.

#3 - A pier lit with 20 LPS fixtures. Seen them off and lit. Pics coming up soon so stay tuned. I was at another pier lit with super boring CFLs. I went there in the afternoon to see the night time at the beach. Saw the other pier 1 mile away. During day time, nothing looked different in term of lighting. Dusk I saw something was off over there. The lights was too yellow to be HPS so I decided to walk over there the next day with my dad. It could be really yellowed HPS lensed fixtures or LPS fixtures from Europe for the US. Europe Lights! They're 35w each. Really interesting to see them lit at night!

#4 - A tunnel somewhere near Baltimore has lots of LPS at the entrances. Supposedly to be 180w each. Unfortunately they were converted to Icetrons according to Jace. At least it's a lot better than HPS.

#1 Belgium highways
#2 Belgium cities and villages, except newest installations (those are HPS)

I believe I saw pictures  from Luxemburg in which are a lot streetlights on the highway too. Which lamps are this exact I can´t remember.

My community College! See here

I can answer this: San Jose, CA! 62,000 street lights, 90% are LPS.

In the Toronto Area,  The Gardiner Expressway and the Don Valley Parkway was lined with what I think were Philips LPS fixtures on aluminum davit poles but they were removed in 2006 and around 2001 respectively so no large installation of LPS fixtures is in my area today.

UPDATE: Pedestrian crosswalks in Ontario are illuminated with LPS lamps mounted inside overhead signs.

2ND UPDATE: There is a small section of Highway 401 near Trenton, Ontario lit with LPS.
            A Home Hardware store near me has the parking lot lit with LPS.
           

In my area it is very rare to see a LPS fixture because Georgia Power doesn't install them.

In my area it is very rare to see a LPS fixture because Georgia Power doesn't install them.

@Lightman64 - mebbe you can get lucky and see them on private parking lots as I have.

UPDATE - Added another LPS find which was the first one to be found. Forgot all about it. 

The town of Massapequa, NY (Long Island). A surprising number of these in use as streetlights.

The Provence of Alberta seems to still have love for LPS.  Driving through, I saw many remote intersections lit with LPS, along with stretches of highway near Edmonton.

I'm currently in New York City, and see many LPS lights lighting underpasses.  Most underpasses I've seen had LPS lights, though a few had HPS and a couple had LED glarebombs.

Yep, San Jose, CA has a TON of LPS streetlights!

Here in Nova Scotia, Canada, we had all provincially owned intersection/highway lighting as LPS. Since a new company that produces LED streetlights opened in the area, the government invested in their product and all luminaires that were once LPS are now LED, with the exception of maybe half a dozen that were missed. A few private yards are lit with one or maybe two LPS lanterns. There is a small hospital near me that is still lit with (18 w ??) LPS lamps.

Medved, you're right, in Belgium, there are lots of LPS. In tunnels, they are abundant, as well as on the highways. I visited a bit in Luxemburg, but only in the daytime and did not notice the lighting. If I remember correctly, Amsterdam has some LPS fittings, although there are lots of HPS as well (if I remember correctly).

Near me is the parking lot of Diamond Ranch High School in Pomona which is lit entirely with 90 watt LPS lamps in Philips/Gardco Form 10 fixtures.

There's also the cities of Hemet and Escondido in southeast Riverside and northern San Diego counties respectively which both use a lot of LPS street lighting due to their proximity (within 39 miles) of the Palomar Observatory.

Guys when i was younger, back in the earlier 1990s, my family and I would travel the Lincoln Tunnel of New York and that was lit with low-pressure sodium's. That is how I became fascinated with them. Some were Orange, some old and flickering, some bright… The fuxtures looked very old then… Would anyone from that area happen to know if they are still there or have been replaced with a different kind of fixture?  I am dying to know, but haven't been through it for over 15 years.

There is a rural town called Stanthorpe, approximately 200 km south-west of Brisbane. In the 1980'e the town was lit almost exclusively by LPS. Nearby townships were lit with the same - most fittings were GEC Z9464 in 90 or 135W configurations. There must have been hundreds in this regional part of Queensland. Now there would be less than a handful still in service in Australia!