how to write about a Table in academic writing task 1

The table shows data about underground railway systems in six major cities with date opened, kilometres of route and passenger numbers per year in millions

First Step
For the writing tasks in IELTS, you always need to re-write the introduction in your own words while keeping the same meaning (paraphrasing). You will need to have good vocabulary for this but not everything needs to be paraphrased. In this particular task, it is pretty straightforward. Using synonyms and changing the sentence structure are two ways to paraphrase successfully.

Paraphrased Version

The table illustrates data regarding underground railways from six large cities in various parts of the world. The information shows when these railways were opened, kilometres of route and yearly passenger numbers in millions.

Second Step

Writing an overview
Having an overview for academic writing task 1 is very important for a good band score. In the overview, you need to summarise the trends or main features. You have to be selective here if the table has a lot of data. Do not write about everything. Pick out the main features.

Do not mention percentages, detail or numbers here. Pick out the key features of the table. The place for the details are the main body paragraphs. Just remember that there should never be a conclusion for academic task 1 writing.
 
Overview
Overall, London and Paris have the oldest underground train system in the world, compared to Los Angeles which started service at the turn of the 21st century. Passenger numbers for Tokyo are the highest, in contrast to Kyoto, which has the lowest number of yearly passengers and the shortest kilometres of route 

Third Step
 
Which tense and what grammar will be used?

The main tense, in this case, is the present tense and the passive voice highlighted in red. We will be comparing the cities and passenger numbers as well as kilometres of railway. Comparatives and Superlatives must be used in the body paragraphs which I have underlined in green below. 

Main Body Paragraphs:

‘The London Underground, which opened in 1863, is the oldest network. It is also the most extensive with 394 kilometres of route. The railway system in Paris was opened in 1900 and is approximately half the size and serves more passengers. Tokyo’s system is the busiest with 1928 million passengers yearly, however, when compared to London, it has a much smaller route at 155 kilometres.

Regarding the three more modern networks, Washington DC was completed in 1976 and has the longest route. In comparison, Kyoto has only 11 kilometres of route and the lowest passenger numbers of all the cities with 45 million passengers yearly. Following this. Los Angeles, which opened in 2001, has 28 kilometres of track and serves 50 million passengers per year.