The adjectives 广阔, 辽阔 and 广大
All three adjectives are used to indicate a large scale, but they have some differences.
The adjective 广阔
广阔 
is used to describe a large area. It is more commonly used to describe geographical objects.
For example, "wide fields", "a big city".
is used to describe a large area. It is more commonly used to describe geographical objects.
For example, "wide fields", "a big city".Examples
飞机失事残骸散落在一个广阔地域
The wreckage of the plane crash is scattered over one large area
fēijī shīshì cánhái sànluò zài yí ge guǎngkuò dìyù
它是广阔沙漠的一部分
It is a part of a vast desert
tā shì guǎngkuò shāmò de yíbùfèn
广阔 can be used with abstract concepts. For example: "broad outlook", "broad view".
Examples
我们的视野令人惊奇地广阔
We are surprisingly open-minded
wǒmen de shìyě lìng rén jīngqí de guǎngkuò
The adjective 辽阔
辽阔 is used to describe bigger areas than the areas described by 广阔. It is used with words like sea, desert, space, or country.
is used to describe bigger areas than the areas described by 广阔. It is used with words like sea, desert, space, or country.Examples
他放眼向辽阔无际的海洋望去
He looked at the endless ocean
tā fàngyǎn xiàng liáokuò wújì de hǎiyáng wàng qù
她曾统治过一个幅员辽阔的帝国
She once ruled a huge empire
tā céng tǒngzhìguò yí ge fúyuán liáokuò de dìguó
思考空间也许很辽阔
The space for reflection can be very wide
sīkǎo kōngjiān yěxǔ hěn liáokuò
The adjective 广大
广大 has two meanings:
1) "wide", "large".
In this case, it describes the size of a territory.
has two meanings:
1) "wide", "large".
In this case, it describes the size of a territory.Examples
开发建设影响了乡村广大地区
Large districts of rural areas have been developed and rebuilt
kāifā jiànshè yǐngxiǎng le xiāngcūn guǎngdà dìqū
世界如此奇妙，世界如此广大
The world is so beautiful, the world is so big
shìjiè rúcǐ qímiào, shìjiè rúcǐ guǎngdà
2) "wide", "numerous".
In this case the adjective is used to describe a large number of something. For example: "broad masses", "large number of complaints".
Pay attention
The word 辽阔 is most commonly used in this meaning.
Examples
这类工作包含广大的中层阶级人士
This type of work involves a wide range of middle-class people
zhè lèi gōngzuò bāohán guǎngdà de zhōngcéng jiējí rénshì
该中心对于广大公众来讲很便利
The center of town is convenient for the general public
gāi zhōngxīn duìyú guǎngdà gōngzhòng lái jiǎng hěn biànlì