ALL AROUND THE THE TOWN there are hundreds upon hundreds of very valuable parcels of real estate with nothing -- or at least, nothing usable -- built on them. How can this be?

The short answer is that these pieces of land are being used as an investment. After all, if you're holding a roll of gold coins, or a rare painting, or a sheaf of stock certificates as an investment, you don't need to DO anything with them, BUILD anything on them -- you can simply hold them, and wait for their value to rise. That's what land speculators do, too.

What's wrong with that? Well, although a piece of prime urban land acts, in the market, just like a unique collectible item, we don't need unique collectible items to build our houses or our businesses on. Not so with land! Look at the examples below (picked out of a menu of many thousands) and imagine how many affordable housing units, profitable storefronts, jobs in construction and retail and all the synergistic effects of a vibrant city are going to waste on them.

1008 Madison Avenue. Here's a nice-looking old building, on the corner of Madison and 77th. Its current lack of a roof makes it somewhat less appropriate for immediate occupancy, but it sold for $23 million in 2006. The city says its current value is $5.48 million, and it pays $63.8K in taxes, or 0.27% of its selling price.

159 Ludlow Street. A cute, 25x43 foot vacant lot, two short blocks from the 2nd Avenue stop on the F train. Note the sidewalk ATM next door. It sold in 2007 for $1.52 million. On this year's rolls, its market value has jumped up to the level of the selling price. This reflects a healthy shift of policy at the Assessor's office. In 2007 its value was listed at $136K, even though it also sold that January for $1.2 million.

Ditmars Blvd., Queens. This 33x72 ft. lot is separated by a wooded buffer from Grand Central Parkway, and is about a half-mile from La Guardia airport. It sold for $1.55 million in 2005. Its property tax bill for 2009, "before abatement," is listed at $749.

State Street, Brooklyn. Brooklyn Heights, a block off Atlantic Avenue, and a stone's throw from the East River, this lot with 125 feet on State Street sold in 2007 for $3.4 million. Clearly the designer of the apartment building next door didn't expect it to be vacant for long.

601-603 Park Avenue. We can't strictly call this one "vacant" -- but it is an amazing deal. This venerable, 1901 building has 100 feet on Park Ave. at 64th Street. It's a private home, a single residential unit, and it sold in 2008 for a mind-blowing $31.8 million. There've been no sales -- yet -- of the three 20-foot wide lots behind it on 64th.

Third Street, Brooklyn. Five lots comprising 200 feet along Third Street were sold for $7.78 million in 2007. According to the city they had a combined market value (including building values) of $1.18 million in 2009.

Woodycrest Avenue, The Bronx. Here's a 100x109 ft. lot, two blocks from Yankee Stadium, whose stately tree-growth attests to how long it's been idle. It's tax-emempt -- and it sold in 2006 for $9.8 million.

Daniel Low Street. Let's not leave Staten Island out! Apparently the honest assessment practice we noted above in Ludlow Street hasn't yet arrived in Staten Island. This 30x100 foot lot sold in 2007 for $585,000, but its market value for 2009 is listed as $251K. It's current tax bill is $453, or 0.07% of the selling price.

Hendricks Street, Staten Island. Despite the six vacant lots on this block, it isn't in some derelict slum neighborhood; it's in staunchly residential, Republican Staten Island. Anyway: the second lot from the right, in between the two houses, sold in 2006 for $460,000; its market value is listed, this year, as $112,500, and its tax bill is $374. The tax bills for the houses next door are both over $2,000.

More Mindblowing Assessment Weirdness: