First, let's understand what "Bhu-Mandala" is in Vedic teachings.

To begin with, Bhu-Mandala is NOT our small earth globe; it is way too expanse and big to be our small earth global sphere (planet)

In the Bhagavat Purana (Srimad Bhagavatam), islands do not only mean land in the sea; the word island also means global planets in the ocean of outer space.

Srila Prabhupada - "The planets are called dvīpas. Outer space is like an ocean of air. Just as there are islands in the watery ocean, these planets in the ocean of space are called dvīpas, or islands in outer space." (CC Madhya 20.218, Purport)

Bhu-Mandala is our entire single 4 billion mile diameter sized material universe according to Srimad Bhagavatam and NOT our earth planet.

Sometimes Bhu-Mandala is called a planetary system, but it is really our entire 4 billion mile sized material universe that houses all the 14 different planetary systems.

Srimad Bhagavatam's 5th Canto describes our universe that is deep inside our surrounding Brahmanda universe, as 500,000,000 yojanas (4 billion miles) in diameter. 

In other words, our small earth globe known as Bhuloka, along with all the 14 planetary systems, are within our 4 billion diameter material universe that can be also called "the Bhu-Mandala universe."

Although some scholars consider "4 billion miles in diameter" as a code because according to NASA, just our Solar System is said to be 24 billion miles in diameter. 

And it takes 4 light years to reach the nearest Solar System Alpha-centauri which equals "24 trillion miles away!"

But, modern science are NOT seeing everything; they are limited to their mundane material senses and speculation however, our material universe being only 4 billion miles in diameter does not seem right either.

As said above, our 4 billion Bhu-Mandala material universe is supposed to situated deep inside the greater outer surrounding Brahmanda universe that surrounds it.

The outer Brahmanda our secondary universe is encased in,  is made up of 7 or 8 layers of material energy (gross and subtle) that are quadrillions of miles thick in diameter.

The seven layers of the Brahmanda is 44 quadrillion, 444 trillion, 444 billion miles in diameter, or twice that size if only measured from the inner edge of secondary universe inside the Brahmanda.

Our massive Brahmanda comes from the body of Maha-Visnu along with billions of other "brahmandas" or cosmic eggs that are almost spherical balls.

This means within each Brahmanda greater universe, there is a secondary smaller universe inside it, as said above, ours is called Bhu-Mandala, it is sometimes called the greater earth Mandala (not to be confused with our small earth globe we live on)

Our Bhu-Mandala universe is an expanse that houses our 14 planetary systems that all together in outer space look like a flat disc of planets.

This is the real meaning of the Bhu-Mandala universe as being flat

Remember, Bhu-Mandala is NOT our earth globe, as some scholars wrongly believe.

Our Bhu-Mandala universe with its 14 planetary systems, is just one material universe out of billions of universes all existing deep inside their surrounding Brahmanda universe as well.

And our small earth globe (Bhuloka) we live on is just a spec within a planetary system within our Bhu-Mandala universe.

Once again, Bhu-Mandala IS this single inner universe we are in that houses all 14 planetary systems.

It is important to understand that Bhu-Mandala is NOT our small Earth globe we live on.

In vaniquotes, Prabhupada tells us that the "small earth" (Our earth planet) fell into the Garbhodak ocean and NOT our entire universe, also known as the larger earth called Bhu-Mandala.

The seven islands of the Bhū-Maṇḍala's 4 billion diameter material universe can be difficult to understand.

One thing is certain: our earth home is a round global sphere in outer space and only fools think it is flat.

As said above, modern Cosmologist do not agree that our material universe is 4 billion miles in diameter when just our solar system alne is said to be 24 billion miles in diameter. 

Some sentimentally claim we are only interested in describing our material universe according to Srimad Bhagavatam.

No, I will question the conclusions of sastra as well if it does not seem right as in this case regarding our universe is just 4 billion mile diameter. 

This needs to be questioned because it may include dimensional realities beyond our vision, but must also be properly answered without speculation and sentimentality, or told to just accept sastra without inquiry or proof-

1.  The definition of Bhū-Maṇḍala and its seven islands or dvīpas meaning planets in outer space.

2. Defining Jambūdvīpa the center realm Bhū-Maṇḍala's universe of 14 planetary systems.

3. Division of Jambūdvīpa into Nine Varṣas (planets in outer space) or Regions

4. Definition of Bhārata-varṣa (our small Earth global sphere) as one of the nine regions in outer space of Jambūdvīpa.

5. The Nine Varṣas or planetary systems are different as the influence of Jambūdvīpa

6. The math and dimensions of Jambūdvīpa that are in the centre of the Bhu-Mandala universe.

7. New Puranic Maps of Jambūdvīpa in relation to the 4 billion diameter.

1. Defining Bhū-Maṇḍala and its seven islands (planets) or dvīpas

The definition of Bhū-Maṇḍala and its centre island Jambūdvīpa has been given in the Śrīmad-Bhāgavatam as follows-

"The planetary system known as Bhū-Maṇḍala resembles a lotus flower, and its seven planets (Dvipas) in outerspace resemble the whorl of that flower. 

The length and breadth of the planetary realm known as Jambūdvīpa, is situated in the middle of the whorl in our 4 billion miles diameter material universe (Bhu-Mandala)

Jambudvīpa has TWO meanings.

1 - India on this "earth planet."

2 -  The greater "earth," our entire 4 billion mile diameter universe called Bhu-Mandala.

The word Jambudvīpa literally refers to "the land of Jambu trees," where jambu (also known as jamun) is the Indian Blackberry.

Dvīpa has two meanings, "island" or "continent" and "planets" situated in the ocean of outer space.

Srila Prabhupada - "The planets are called dvīpas. Outer space is like an ocean of air. Just as there are islands in the watery ocean, these planets in the ocean of space are called dvīpas, or islands in outer space." (CC, Madhya 20.218, Purport)

Our earth planet is not flat that some foolish ignorant devotees wrongly believe. 

The "world" (the word "world" here means our Bhu-Mandala universe) is divided into seven concentric island continents (planets in outer space)

(sapta-dvipa vasumati) separated by the seven encircling oceans of solar winds in outerspace, each double the size of the preceding one (going out from within)

The seven continents (planets) of the Puranas are stated as Jambudvipa (which is also India on this plane, 

Plaksadvipa, Salmalidvipa, Kusadvipa, Krouncadvipa, Sakadvipa, Pushkaradvipa.

Seven intermediate oceans on the planets above existing in outerspace consist of 

salt-water, 

sugarcane juice, 

wine, 

ghee, 

yogurt, 

milk, 

water. 

The mountain range called Lokaloka is on the outer edge of our Bhu-Mandala universe.

The Bhu-Mandala universe is also called Earth and means "world-no-world."

Bhu-Mandala stretches across the sea, which means the ocean of outer space. 

There are also different types of oceans on the many planets in outer space that exist in our Bhu-Mandala universe that houses the 14 planetary systems..***..