Taiping is the largest natural feature in the Spratlys, with an area of about half a square kilometre. It has been occupied by the Republic of China (ROC) government, based in Taipei, since 1956, while also being claimed by the People’s Republic of China (PRC) government in Beijing, the Philippines and Vietnam.

A maritime feature classified as a rock carries with it entitlement to a territorial sea extending out 12 nautical miles, but does not get an exclusive economic zone (EEZ), with a radius of 200 nautical miles, or further rights.

If no feature in the Spratlys is entitled to an EEZ, the surrounding countries – the Philippines, Malaysia, Brunei and Vietnam – could each simply draw EEZ lines from their own major islands or coasts into that part of the South China Sea and claim the respective rights. But if Taiping is considered an island, the ROC and PRC, which inherited the ROC’s territorial claims in 1949, would enjoy EEZ rights around it, giving them overlapping EEZ claims in the South China Sea with the Philippines and other claimants.

Taiping is occupied by the ROC, which is not recognised as sovereign country by the United Nations, the PCA, or either of the parties involved in the case. They all consider Taiwan part of the PRC, so even without physically occupying Taiping, Beijing could still claim its EEZ.

Indeed, in its official response to the case brought by the Philippines, Beijing said in 2014 that Manila had violated the “one China” principle by deliberately excluding Taiping from “Chinese occupied or controlled” islands in its requests to the PCA.

Taiping is only 199 nautical miles from the Philippines’ Palawan Island but the Taiping issue was not included in the first Philippine submissions and was instead raised in merit hearings late last year, after the release of Beijing’s 2014 position paper.

The Philippines argued Taiping has neither civilian habitation nor sustainable economic life, because it is a military garrison and relies on outside supplies.

In response, then Taiwanese president Ma Ying-jeou flew a team of international journalists there in March to prove it was habitable.

How the island’s new president, Tsai Ing-wen, will react to any PCA ruling on Taiping will be closely watched.

Will the “nine-dash line” be declared invalid?

The U-shaped, nine-dash line encircling most of the South China Sea is the core of China’s claim, and the centre of controversy.

It was first published on a map drawn by the ROC government in 1947 and then inherited by the PRC in 1949, but neither of them have had effective control over the entire area.

Beijing claims sovereignty over all land features inside the line, and in individual cases has referred to the line to claim vague “historical” maritime rights. However, it has never clarified the line’s meaning in legal terms, or what kind of entitlements it wants within it.

The Philippines has asked the tribunal to reject Beijing’s possible claims to sovereign rights and jurisdiction, and to “historic rights” within the area encompassed by the line.

Manila has said the line exceeds the geographic and substantive limits of maritime entitlements under the UN Convention on the Law of the Sea (UNCLOS), such as a territorial sea, EEZ, and so on, and therefore has no legal effect.

Beijing has said it will ignore any rulings by the PCA.

Will mainland China’s activities in the South China Sea be deemed to be damaging the environment (and will it be told to stop)?

The tribunal has said it has the authority to judge whether Beijing has violated its duty to protect and preserve the marine environment at Scarborough Shoal and Second Thomas Shoal.

In addition, the tribunal may also consider whether Chinese construction projects at Mischief Reef have damaged the marine environment, as argued by the Philippines.

The Philippines presented evidence that it said proved “illegal and unregulated” Chinese fishing and massive island building activities had damaged the ecological systems of coral reefs, endangered species such as turtles and sharks, and caused maritime pollution.

If such activities are found to be in breach of UNCLOS, the same logic might be applied to similar activities at other islands or reefs that are also part of what has been dubbed the “Great Wall of sand”.

Will four of the islands controlled by Beijing (Scarborough Shoal, Johnson Reef, Cuarteron Reef and Fiery Cross Reef) be defined as “rocks”?

The tribunal will decide if each of these land features qualifies for having an exclusive economic zone.

If the tribunal specifically declares they “generate no entitlement to an exclusive economic zone or continental shelf”, Beijing would not be able to share EEZ rights with countries controlling nearby islands.

In particular, if Scarborough Shoal, which is not part of the Spratlys, is deemed a “rock” it would fall into the EEZ of the Philippines’ Luzon Island, which is about 125 nautical miles away. The Philippines would have legal grounds to exercise rights to fishery, oil and gas resources and scientific research in nearby waters, even though mainland China took control of the shoal in 2012.

Will mainland China’s two largest artificial islands be defined as “low-tide elevations”?

Mischief and Subi reefs have become the two biggest land masses in the South China Sea after massive reclamation in the past couple of years. Mischief is now more than 10 times the size of Taiping.

If the tribunal says they are naturally low-tide elevations, which only emerge above water at low tide, the two major Chinese bases in the Spratlys would have no territorial sea, EEZ, or other rights. Instead, they could only claim a 500-metre safety zone surrounding them.

Moreover, without entitlements of their own, they would fall into the EEZ of nearby islands. Since the EEZ rights holder is entitled to jurisdiction over the establishment and use of “artificial islands, installations and structures” in the EEZ, other countries, including the Philippines, would have an endorsement to challenge the legitimacy of China’s constructions on Mischief and Subi.

Will two Chinese-occupied reefs be included in the territorial sea of Vietnamese-controlled islands?

Gaven and McKennan (Hughes) are two small reefs within 12 nautical miles of the islands of Namyit and Sin Cowe, respectively. Beijing, Taipei and Hanoi claim all four of them.

The Philippines asked the tribunal to declare the two Chinese-occupied reefs “low-tide elevations” without territorial sea, contiguous zone or EEZ, and to use them when measuring the territorial sea of Namyit and Sin Cowe islands, both occupied by Vietnam.

If a low-tide elevation lies within an island’s 12-nautical-mile territorial sea, UNCLOS allows the territorial sea to be extended for another 12 nautical miles starting from the elevation – if the elevation and the island are undisputedly owned by one state.

If the tribunal supports the second half of the Philippine demand, Vietnam, an unmentioned third party in the arbitration, would find itself with an unexpected advantage in those particular territorial contests.

Will Beijing’s administrative and law enforcement in the disputed shoals be ruled unlawful?

The Philippines accused the mainland Chinese authorities of impeding Filipino fishermen near Scarborough shoal, and doing so in a dangerous manner.

Manila also accused Beijing of interfering with the resupply of a Philippine warship intentionally grounded at Second Thomas Shoal, which Beijing threatened to remove a couple of weeks ago.

These submissions are arguably related to more complicated territorial sovereignty issues, over which Beijing says the tribunal does not have jurisdiction.