hi Adhisti, actually I want to comment about your task responses, but unfortunately you did not put a picture for this essay. Therefore, I am going to suggest your writing, especially when it comes to grammatical errors and your flow sentences.
Grammatical issues :
I have expected that I can find a perfect grammar in your writing. As a matter of fact, I have found several grammatical errors here although I presume that it is owing to a lack of carefulness.
it can be seen that there were a gradual rise of the population
it should be = there was a gradual rise in the population...more significantincrease
more significant increasesPopulation stood at 75 thousand in 1940, which was higher than Columbia and Yamhill.
you should put an article before "population" unless this is a new topic. Nevertheless, I bet that you will get a wrong flow sentence when you pu a new topic here.a leadingcountie
becareful with your spelling, it should be"continue"FLOW SENTENCE, IDEA:
during 1940 to 2000
you can change it becoming = over a 60-year period.
Oregon had three counties and population was measured in thousands in each counties
why you use pas perfect here?, I know that that graph is in the past but I think you cannot use past tense in your introductory paragraph. I mean that it will be better if you use present tense in your introductory paragraph whereas the data is in the past
Overall, it can be seen that there was a gradual rise of the population in three different counties of Oregon.
I think that your overview is too general inasmuch as you just give an interesting trend without comparison. According to the task in every IELTS writing task one is asking us to compare where possible. Thus, I would argue that you should compare a trend in your overview.
Then, they rose gradually in 1970 and again it grew rapidly in the following thirty years.
to vary your tense you can use pas perfect if you wish. this is my example:
"by 170 it had gradually risen in the reminder of the time."Washington had more significant increase than other two counties. Population stood at 75 thousand in 1940,
the population in Washington was two times higher than....
KEEP STUDY AND KEEP SPIRIT. ;)