Investments in real estate properties are presented at cost, and consist of the following (in thousands):


	March 31, 2013		December 31, 2012
Industrial operating properties (1):
Improved land	$	4,063,059	$	5,317,123
Buildings and improvements		13,458,016		17,291,125
Development portfolio, including cost of land (2)		884,352		951,643
Land (3)		1,754,053		1,794,364
Other real estate investments (4)		436,328		454,868

Total investments in real estate properties		20,595,808		25,809,123
Less accumulated depreciation		2,292,946		2,480,660

Net investments in properties	$	18,302,862	$	23,328,463

(1)

At March 31, 2013 and December 31, 2012, we had 1,647 and 1,853 industrial properties consisting of 259.8 million square feet and 316.3 million square feet, respectively. In 2013, in connection with our two new ventures in Japan and Europe, we contributed 207 properties with a net carrying value of $4.6 billion, consisting of 58.3 million square feet for gross proceeds of $4.9 billion. See Note 4 for further discussion on these transactions.

(2)

At March 31, 2013, the development portfolio consisted of 34 properties aggregating 15.6 million square feet under development with estimated completion dates primarily in 2013 and 2014 and 8 properties aggregating 2.6 million square feet of pre-stabilized completed properties. At December 31, 2012, the development portfolio consisted of 30 properties aggregating 13.2 million square feet that were under development and 15 properties aggregating 4.8 million square feet that were pre-stabilized completed properties.

(3)	Land consisted of 10,605 acres and 10,915 acres at March 31, 2013 and December 31, 2012, respectively, and included land parcels that we may develop or sell depending on market conditions and other factors.

(4)

Included in other investments were: (i) certain non-industrial real estate; (ii) our corporate office buildings; (iii) land parcels that are ground leased to third parties; (iv) restricted funds that are held in escrow pending the completion of tax-deferred exchange transactions involving operating properties; (v) certain infrastructure costs related to projects we are developing on behalf of others; (vi) costs related to future development projects, including purchase options on land; and (vii) earnest money deposits associated with potential acquisitions.