Gemara

(Shmuel): If one sold 10 fields in 10 lands, once the buyer acquires one through Chazakah, he acquires all of them.

Bava Basra 53b (Rav Asi): If there was a fence between two (Hefker) fields, and Reuven was Machzik in one field to acquire both, he acquires only that field.

54a (Rav Huna): If one digs any amount in a field surrounded by fences, he acquires the entire field.

(Shmuel): He only acquires where he digs.

Question: (According to Rav Huna,) if the field is not surrounded by fences, how much does he acquire through one insertion of the shovel?

Answer (Rav Papa): He acquires the length of a standard furrow.

Kidushin 27a (Rava): This (acquiring Metaltelim Agav land) works only if all the money was given. If only part was given, he acquires according to what he paid.

Support (Beraisa): In some ways, Chazakah is stronger than money or a document. One can acquire 10 fields in 10 lands through one Chazakah. This is only if he paid for all of them. If not, he acquires only according to what he gave.

This Beraisa also supports Shmuel.

(Shmuel): If one sold 10 fields in 10 lands, once the buyer acquires one through Chazakah, he acquires all of them.

Bava Metzia 77b (Beraisa #1): Reuven sold a field to Shimon for 1000, and Shimon paid 200. If Reuven retracts, Shimon has the upper hand. He can demand his money back, or take Idis (best quantity land) worth 200. If Shimon retracts, Reuven has the upper hand. He can return the money, or give Ziburis (worst quantity land) worth 200.

R. Shimon ben Gamliel says, we teach them not to retract. Rather, they write a document of sale saying that Shimon still owes 800, which he may pay later.

Contradiction (Beraisa #2 - R. Shimon ben Gamliel): If Levi bought land and paid half of the price, he acquired it all. He can give the rest of the money years later.

Answer: In Beraisa #1, the seller pursues the buyer to get the money. (This shows that he sold only because he needs the money. Since Shimon cannot pay the full amount, he does not acquire, unless they write...) In Beraisa #2, the seller does not pursue the buyer (so Shimon acquires);

(Rava): If the seller pursues the buyer, the buyer does not acquire (unless he pays right away). If the seller does not pursue the buyer, the buyer acquires.

Rishonim

Rif and Rosh (Kidushin 1:36): Shmuel taught that if one bought 10 fields in 10 lands, once he acquires one through Chazakah, he acquires all of them. Rava said that this is only if all the money was given. If only part was given, he acquires only according to what he paid. A Beraisa supports Rava.

Ran (DH Omar): In our texts, Rava discusses Agav. He teaches that one acquires Metaltelim Agav land only according to what he paid for the Metaltelim. The Beraisa (a Chazakah to acquire 10 fields in 10 lands acquires only according to what he paid) supports him. Acquiring Metaltelim Agav is like acquiring another field far from the field on which he does Chazakah. The Rif explains that Rava discusses buying just fields. Also the Rambam (Hilchos Mechirah 3:8) did not stipulate that Agav works only if he paid for the Metaltelim. Perhaps they had a different text. The Gemara did not say that he acquires only according to what he paid, only when the seller pursues the buyer. Rather, it is in every case. This is because Agav is a weak Kinyan. When the seller pursues the buyer, this is like one who gave part of the money. Whoever retracts has the lower hand, like it says in Bava Metzia 77b.

Rosh (Bava Metzia 6:8): A Chazakah on one field to acquire 10 scattered fields acquires according to how much he paid (Kidushin 27a). This is even if the seller does not pursue the buyer, for a Chazakah here does not help for a field elsewhere unless he paid for it.

Rambam (Hilchos Mechirah 1:19): If one sold 10 fields in 10 lands, once the buyer makes Chazakah in one of them, he acquires all of them. This is even if one was a tall mountain and the other was a gorge, which have different uses.

Rambam (20): This is if he gave all the money. If not, he acquires only according to what he paid. Therefore, if it was a gift, he acquires all of them.

Rosh (Bava Basra 3:60): If there was a fence between two fields, and one was Machzik in one field to acquire both, he acquires only that field. This refers to Hefker property. If a buyer paid for all the fields, even if they are in 10 lands, he acquires all of them. A gift is like a sale in which he did not pay. However, if the giver said to acquire all of them through one Chazakah, he does. A Tosefta (2:11) teaches that a Chazakah in one of 10 Hefker fields acquires all of them. If one bought 10 fields, a Chazakah in one acquires all of them. Why did the Tosefta teach these separately? The Ramban says that the Seifa should say 'in 10 lands', like Kidushin 27a. The Hefker fields are adjacent. If there is no divider between them, why are they considered 10? Perhaps we call 'one field' the length of a furrow. He acquires all only if he stipulated. If not, he acquires only a furrow's length.

Rosh (64): The Halachah follows Rav Huna, for the question of a field without borders is according to him. Also, Rav Nachman ruled like him (55a).

Poskim

Shulchan Aruch (CM 192:12): If one sold 10 fields in 10 lands, once the buyer makes Chazakah in one of them, he acquires all of them. This is even if one was a tall mountain and the other was a gorge, which have different uses. This is if he gave all the money. If not, he acquires only according to what he paid.

Beis Yosef (DH v'Chosav ha'Rosh beha'Umnim): R. Yerucham says that if the seller told the buyer to make Chazakah in one field for all of them, he acquires all of them even if he did not pay.

SMA (19): Ir Shushan says that if the fields are near each other, one Chazakah acquires all of them even if he did not pay for all of them. The Tur and Rosh say oppositely.

Shulchan Aruch (ibid.): Therefore, if it was a gift, he acquires all of them.

Beis Yosef (DH v'Chosav ha'Rambam...): This is like the Rambam and R. Chananel. We follow them against the Rosh.

Rema: Some disagree regarding a gift. Likewise, 10 houses, or a house and a field are like 10 fields.

SMA (24): This opinion holds that since the giver receives nothing, he wants to be able to retract as long as the receiver did not acquire. Even this opinion agrees that one who rents acquires all the fields through one Chazakah even before paying anything, for rental is not due until the end.

Gra (19): This opinion (the Rosh) holds like Answer #2 in Tosfos (the strength of Chazakah over money is that it acquires when the seller owed the money). The Rosh's text said that Rava discussed acquiring many fields. In our text, Rava discusses Agav. One can acquire a gift of Metaltelim Agav, and Rava equates this to fields in different places.