Esta circunscripción es grande.

Because circunscripción is a feminine singular noun, and the demonstrative has to agree with it.

• este = masculine singular
• esta = feminine singular

So:

• este distrito
• esta circunscripción

You learn its gender as part of the noun: la circunscripción.

There is also a very helpful pattern here: nouns ending in -ción are almost always feminine in Spanish.

Examples:

• la nación
• la elección
• la administración
• la circunscripción

So once you see -ción, feminine is a very good guess.

Because esta is already acting as the determiner.

In English, this already fills that slot, and the same is true in Spanish:

• esta circunscripción = this constituency / this district

You normally do not say la esta circunscripción in standard Spanish. It is either:

• la circunscripción = the constituency
• esta circunscripción = this constituency

Because grande is being presented as a general, descriptive characteristic of the constituency, so Spanish uses ser.

• es grande = it is large / big

Spanish often uses ser for defining or identifying characteristics, and estar more for states, conditions, or location.

Here, Esta circunscripción es grande sounds like a neutral description of size.

If you said está grande, that could sound more marked and context-dependent, sometimes more like it has become big or it is rather big, depending on context.

Because in Spanish, descriptive adjectives often come after the noun.

So the normal order is:

• circunscripción grande

In this sentence, that adjective stays after the noun even though the full structure is:

• Esta circunscripción es grande

Also, when grande comes before a noun, it can change nuance. For example, gran often means great or important, not simply physically large.

So for straightforward size, grande after the noun or after ser is the normal choice.

Because grande is one of the adjectives that has the same singular form for masculine and feminine nouns.

So you get:

• un distrito grande
• una circunscripción grande

It only changes for number, not for gender:

• singular: grande
• plural: grandes

Compare that with an adjective that does change for gender:

• pequeño
• pequeña

In standard Spain Spanish, it is roughly:

cir-cuns-crip-CIÓN

The stress is on the last syllable: -ción.

A rough pronunciation guide for most of Spain is:

• cir with a th sound at the start, like thin
• ción also with that th sound before the final on

So in much of Spain, it sounds approximately like:

theer-koons-kreep-THYON

That is only an approximation for English speakers, but the key points are:

• stress the last syllable
• pronounce ci as a th sound in most of Spain

It shows where the stress goes: circunscripCIÓN.

This matters because without the written accent, Spanish stress rules would make you expect the stress somewhere else.

So the accent tells you clearly:

• not circunscriPCIon
• but circunscripCIÓN

The accent mark is about pronunciation, not about changing the meaning here.

In modern standard Spanish, esta is normally written without an accent mark.

Older usage sometimes wrote ésta when it was a pronoun, but current standard spelling generally avoids that accent except in rare cases of ambiguity.

In your sentence, esta is a demonstrative determiner because it goes directly before the noun:

• esta circunscripción

So esta is the standard spelling here.

You would change every word that needs to agree:

• Esta → Estas
• circunscripción → circunscripciones
• es → son
• grande → grandes

So the plural sentence is:

Estas circunscripciones son grandes.

This is a good example of how agreement works in Spanish across the whole sentence.