"Squashed" maps

[hugovk]

My maps look great, but also a bit squashed. If I plot it with Helsinki's bounding box:

p2a <- plot_map(data, lon_min = 24.8312, lon_max = 25.2022, lat_min = 60.1301, lat_max = 60.2893)

I get a map like this:

When it normally looks more like this:

http://maps.stamen.com/#toner/11/60.1934/25.0715

Do you know what accounts for this, and how I could square it off? Thanks!

[marcusvolz]

That's strange, the addition of coord_equal() should provide the true aspect ratio. Could you provide your data?

[hugovk]

Here's a single coastal route: 20130902-171543-Ride.gpx.zip

On Strava it looks like this:

> data <- process_data('.')
> p1 <- plot_facets(data)
> ggsave("plots/facets003.png", p1, width = 20, height = 20, units = "cm")
> p2a <- plot_map(data, lon_min = 24.8312, lon_max = 25.2022, lat_min = 60.1301, lat_max = 60.2893)
> ggsave("plots/map003.png", p2a, width = 20, height = 20, units = "cm", dpi = 600)

Which produces this facet:

But this map:

[marcusvolz]

The facet uses scales = "free" and doesn't use coord_equal, so it will scale to fill out the facet. The map uses coord_equal, so the x and y axes have the same relative scale (i.e. one unit on the x-axis is the same length as one unit on the y-axis).

From the raw data it looks like the ranges are [60.14653. 60.16568] and [24.920093, 24.961935], so it looks like the map is being plotted correctly - maybe the data has been corrupted?

As a temp solution you can just remove coord_equal from the map code and then manually resize the plot in RStudio before saving.

[hugovk]

I think the data is fine, the first map is from 7 years of data and different devices, and if some were corrupt I'd expect the map as a whole to show more square, with some odd points. But the map as a whole looks accurate, except being "squashed".

The last file uploads and shows fine on GPSies:

Those ranges look correct. Here's one corner of those ranges, 60.14653N, 24.920093E:

And the other one, 60.16568N, 24.961935E:

So I guess what's going on is the "normal" maps aren't being plotted with 1:1 units. Looking at this next map from here shows nice squares, but one grid in one direction is 0N0.50, and to the other is 0E1.00:

I wonder why that is?

[hugovk]

Of course, the reason is the earth is a sphere and flat maps are projections. At the equator one degree of lat/lon are roughly equal. As we go further north, one degree of latitude gets to zero. At 60N, we're 2/3 up.

So we probably want to scale the latitude by how far away from the equator we are.

[hugovk]

It's as easy as using ggplot2::coord_map() instead of ggplot2::coord_equal() to fix it!

[marcusvolz]

Thanks for figuring this out. It makes sense, Helsinki is further from the equator than Melbourne which is why my one didn't seem to be particularly distorted.