The following table summarizes the Partnership’s real property interests (in thousands):

	March 31, 2019			December 31, 2018
Land	$	131,731		$	128,302
Real property interests – perpetual		104,518			101,343
Real property interests – finite life		404,851			416,080
Construction in progress		35,456			29,556
Total land and real property interests		676,556			675,281
Accumulated amortization of real property interests		(40,926	)		(39,069	)
Land and net real property interests	$	635,630		$	636,212

On January 4, 2019, the Partnership completed the sale of its real property interest held for sale as of December 31, 2018 for total consideration of $13.5 million. We recognized a gain on sale of real property interest of $5.9 million upon completion of the sale.

During 2017, the Partnership started developing an ecosystem of technologies that provides smart enabled infrastructure (“FlexGrid^TM”) including smart poles and digital outdoor advertising kiosks across North America. Smart poles are self-contained, neutral-host poles designed for wireless carrier and other wireless operator collocation. The smart poles are designed for macro, mini macro and small cell deployments and will support Internet of Things (IoT), carrier densification needs, private LTE networks and other wireless solutions. During the year ended December 31, 2018, the Partnership completed construction on four FlexGrid^TM infrastructure sites totaling $1.5 million. As of March 31, 2019 and December 31, 2018, the Partnership’s $35.5 million and $29.6 million, respectively, of construction in progress primarily related to the construction of the FlexGrid^TM solution and other projects.

In December 2016, the Partnership formed a joint venture to acquire real property interests that are leased to companies in the outdoor advertising industry located in the UK and Europe. Our venture partner provides acquisition opportunities and asset management services to the consolidated joint venture. As of March 31, 2019, the consolidated joint venture had 139 tenant sites and one investment in receivable with total net book value of $54.9 million. During the three months ended March 31, 2019 and 2018, the consolidated joint venture generated rental revenue of $1.2 million and $0.6 million, respectively.

The Partnership applies the asset acquisition method to all acquired investments of real property interests for transactions that meet the definition of an asset acquisition. The fair value of the assets acquired and liabilities assumed is typically determined by using Level III valuation methods. The most sensitive assumption is the discount rate used to discount the estimated cash flows from the real estate rights. For purposes of the computation of fair value assigned to the various tangible and intangible assets, the Partnership assigned discount rates ranging between 6% and 20%.

The following table summarizes final allocations for acquisitions during the three months ended March 31, 2019 and the year ended December 31, 2018 of estimated fair values of the assets acquired and liabilities assumed (in thousands).

			Investments in real		In-place lease		Above-market		Below-market
Period	Land		property interests		intangibles		lease intangibles		lease intangibles			Total
2019	$	2,330	$	3,640	$	248	$	76	$	(23	)	$	6,271
2018		16,646		91,314		7,939		1,309		(2,031	)		115,177

Future estimated aggregate amortization of finite lived real property interests for each of the five succeeding fiscal years and thereafter as of March 31, 2019, are as follows (in thousands):

2019 (nine months)	$	8,841
2020		11,068
2021		10,451
2022		10,087
2023		9,989
Thereafter		313,489
Total	$	363,925

The weighted average remaining amortization period for non‑perpetual real property interests is 42 years as of March 31, 2019.

During the three months ended March 31, 2019, two of the Partnership’s real property interests were impaired and recognized impairment charges totaling $0.2 million. The carrying value of each real property interest was determined to have a fair value of zero. There was no impairment during the three months ended March 31, 2018.

In March 2019, the Partnership entered into a plan to sell certain real property interests and investments in receivables. The Partnership determined that the sale did not meet the criteria for discontinued operations presentation as the plan to sell did not represent a strategic shift that would have a major effect on its operations and financial results. As a result of this classification, the assets and liabilities were separately presented as AHFS and liabilities associated with AHFS in the consolidated balance sheet as of March 31, 2019.

The carrying amounts of the major classes of assets and liabilities that were classified as held for sale are as follows (in thousands):

	March 31, 2019		December 31, 2018
Land	$	416	$	1,286
Real property interests, net		11,626		5,566
Investments in receivables, net		8,331		—
Other intangible assets, net		75		994
AHFS	$	20,448	$	7,846
Other intangible liabilities, net	$	180	$	397
Liabilities associated with AHFS	$	180	$	397