An American pal and her sister spent a few days here recently. A circuitous route to avoid some roadworks took us past Oxford Airport. Or, as I remarked, what locals still call Kidlington Airfield. I mean, the aircraft using it are twelve or twenty seaters.

‘Oh,’ says my pal, ‘big planes then.’ There was a ‘beg pardon?’ pause from me and a laugh from the car’s back seat. You see, these friends grew up in rural Alaska. As far as they’re concerned, a small plane is one where it’s just you and the pilot. Twelve seats? Luxury travel! Because normal is what you grow up with. As you can imagine, that led to a very interesting conversation.

And as is the way with authors, it’s started me thinking about the issues around local values when it comes to descriptive writing. I recall a conversation some time after Northern Storm was first published. In a bar, so after I’d given either a university or local SFF society talk. In that particular book, the magewoman Velindre spends time both in Einarinn’s frozen northlands, and later, in the tropical Aldabreshin Archipelago. The former is ‘bitterly cold’ and the latter is ‘oppressively hot’. I don’t recall what started the conversation but we were discussing exactly what those terms meant to us personally – and why I, as the writer, hadn’t included specific details to make it clear what a thermometer would say.

The first and most obvious answer is because I didn’t need to. With regard to ‘bitterly cold,’ the reader needs to know there’s snow on the ground and water is frozen. There was no plot or character related reason for me to indicate whether the temperature was minus three degrees or minus thirteen. Even a short paragraph going into more detail would have been wasted words and as far as I am concerned, every word in a book must count.

But it goes beyond that. My personal assessment of ‘bitterly cold’ is going to be very different to my Alaskan friend’s. Just as ‘oppressively hot’ means something entirely different to an author friend who lives in Hawai’i. At World Fantasy Con in San Diego a few years back, she was sitting in the full sunshine in a cardigan and considering getting a jacket while those of us just in from a UK October were grabbing all the shade we could find, sweltering in the most lightweight clothing we owned.

So going back to Northern Storm, adding more precise detail to either of those descriptions could well have been actively counterproductive. Specifying ‘oppressively hot’ in my own personal terms could very easily throw a reader used to a different climate right out of the story. Because their instinctive reaction would be ‘Wait, what? No, that’s not hot weather!’ And even something as apparently trivial as that could undermine the whole book for them. Because if a reader can’t believe in the background detail, how are they going to believe in the wizards and dragons?

On the other hand, you can turn this issue of local values to your writerly advantage, in the right place, for the right character. When I said minus three degrees or minus thirteen a few paragraphs back, I meant Celsius, because my local weather values are centigrade. When I come across temperatures given in Farenheit in US crime fiction, I always have to pause and do a quick mental conversion calculation. It disrupts the flow of my reading, so as far as I am concerned, that’s a bad thing.

But if I was a character in a book? If the author wanted to convey someone feeling unsettled and out of their usual place? Sure, that author could tell us ‘She felt unsettled by the unfamiliar numbers in the weather forecast’ but you could do so much more, and far more subtly, as a writer by showing the character’s incomprehension, having her look up how to do the conversion online, maybe being surprised by the result. It gets how cold in Minnesota in the winter?

It doesn’t just have to be about the weather. How about food? Anyone in the UK who travels to different cities and eats in Indian restaurants will know how much the chilli scale on menus varies. As I can attest from personal experience, what’s ‘medium hot’ in Bradford is a world away from ‘medium hot’ in Blandford Forum. There’s a lot a writer can do with that sort of thing.

It’s also worth checking your own local values/understanding against any historical or other background facts and resources you may be using. I was once attending a convention panel discussing the ancient world, when a genuinely baffled audience member sought clarification after a speaker discussed issues arising from the impossibility of telling slaves from free citizens in ancient Athens. But surely, the colour of their skin…? Because that questioner’s knowledge of slavery was entirely US-based and she was assuming central aspects of that were historically universal. Not so, by any means.

That’s perhaps an extreme example, but for instance, I’ve been caught out – though thankfully in a book’s planning phase, not in print – when assumptions I’ve made about growing and harvest seasons, based on my experience living in the UK, turned out to be nonsensical for the different climate and latitudes where I was setting some action.

So it really is worth taking a little time to consider what that well-known online phrase ‘Your Mileage May Vary’ could mean in relation to your writing, for readers and for characters.