[R-sig-Geo] resolution of openmap() raster layers

Agustin Lobo alobolistas at gmail.com
Fri Feb 26 12:27:34 CET 2016

Can I remove the buttons for saving to a bmp file?
What attribution should be used for publishing?

On Thu, Feb 25, 2016 at 7:42 PM, Chris Reudenbach
<reudenbach at uni-marburg.de> wrote:
> Hi,
> if you just want to map the data, mapview could be an option that among
> others avoid the pixel stretching.
> require(mapview)
> require(raster)
> nica <- getData("GADM", country="NIC", level=0)
> mapview(nica)
> mapview(nica,zcol = "POP2000", color = "#FFA500", lwd= 5, alpha.regions =
> 0.4)
> cheers Chris
> Am 25.02.2016 um 18:49 schrieb Barry Rowlingson:
>> On Thu, Feb 25, 2016 at 5:11 PM, Agustin Lobo <alobolistas at gmail.com>
>> wrote:
>>> Is there any way to download the raster layers
>>> of openmap() with an increased resolution?
>>> I find the quality of the labels very low,
>>> or am I doing something wrong? i.e.
>>> require(raster)
>>> require(mapmisc)
>>> nica <- getData("GADM", country="NIC", level=0)
>>> nicabg <- openmap(nica, path="landscape")
>>> plot(nicabg)
>>   Map tiles from OpenStreetMap and other map tile providers are images
>> designed to be shown at a fixed resolution. When you plot them in an R
>> graphics window you could be stretching them so that each pixel in the
>> original maps to 1.273 pixels on your screen. So some kind of
>> interpolation or nearest neighbour replacement has to be done, and
>> this makes text labels look bad. Other line work will look bad too.
>>   If you try and download more map tiles at a higher resolution then
>> you'll find the labels are now way too small, because what you've
>> downloaded are map tiles designed for a higher zoom level on a web
>> browser. Web map browsers have a fixed set of zoom values that
>> correspond to the resolution of the map tiles. With an R window, you
>> are free to choose odd zoom factors that give the ugly behaviour.
>>   If you can resize your R window exactly right then you might get
>> something that looks good!
>>   The alternative is to build a background map yourself from
>> OpenStreetMap *vector* data and some code and some styling. Or use a
>> map tile provider that doesn't have text labels and add them to
>> selected places with R graphics commands. Lines and polygons will
>> still be stretched and a bit "jaggy" but our eyes don't notice this as
>> much as badly scaled text.
>> Barry
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