apples with pears

アジアの一番の大都市はどこであるかという議論が起こっているそうです。apples with pearsはイギリスの俗語で「階段」という意味のapples and pearsのもじりで，これはstairsの押韻俗語です（『ジーニアス英和大辞典』大修館書店）。おどけて俗語を使っているところに，「形式的に区分けしているが，実質を伴っていない」というニュアンスが感じ取れます。（Sugiuchi）
Defining the borders of a city is no easy task - and there is no international standard to ensure consistency.
Three scholars who in 2009 compared eight different lists of top cities by population, found there were 30 "top 20 cities" in total.
One of them, Richard Greene, associate professor of geography at Northern Illinois University in the United States, says even the most authoritative list, from the UN, "compares apples with pears".
http://www.bbc.co.uk/news/magazine-16761784