Where to find an accurate Mercator Projection world image?

Question

I'm sorry if this doesn't fit "Earth Science" too well. No idea where else to ask this!

Can anyone help me find an accurate world map in Mercator Projection? It doesn't need political borders or too much detail, just coastlines would do. (Ideally with land coloured buff and sea coloured blue, but I'm not picky!) I would be happy to pay, if it isn't too much - unless there are free resources out there!

I'm writing a modelling application where I need to plot Lat and Lon on a world chart so it needs to be fairly accurate (if you call Mercator Projection accurate).

Thanks for any help, and sorry if I've broken any rules here.

Answer 1

So here is the way I do that personnally with NaturalEarth data and R (but you can do something similar i m assuming with any programming language that can deal with GIS or any GIS software):

Fist download and unzip the file:

download.file("http://www.naturalearthdata.com/http//www.naturalearthdata.com/download/10m/physical/ne_10m_coastline.zip", "10m_coast.zip")
unzip("10m_coast.zip")

Then reads in the shapefile:

library(rgdal)
library(maptools)
a <- readShapeSpatial("ne_10m_coastline.shp",CRS("+proj=latlon +ellps=GRS80"))

Then project it:

a_merc <- spTransform(a,CRS("+proj=merc +ellps=GRS80"))

And plot it:

pdf(w=20,h=20,file="merc.pdf")
par(mar=c(0,0,0,0))
plot(a_merc,asp=1,xaxs="i",yaxs="i")
dev.off()

This is a very minimalist example of course, it only draws the coastlines (as a line by opposition to drawing the continents as polygons, that would allow a more advanced colouring scheme but the projection to mercator of polygons is more complex, as Antarctica creates problems).

Answer 2

You can use Generic Mapping Tools (GMT): http://gmt.soest.hawaii.edu/

It's a command line tool for (among other things) plotting maps and geographical data. Works best on Linux/Mac but also on Windows.

Here's an example. Running this code generates a map:

gmt pscoast -R0/360/-80/85 -JM20 -B20/10 -Di -Glightbrown -Slightblue -Wblack > merc.ps

And this will convert to png:

ps2raster merc.ps -Tg -A -P

Resulting in this:

It's highly customisable and easy to use!

Answer 3

Natural Earth is a public domain, map dataset available at 1:10, 1:50, and 1:110-million scales. Announced at the 2009 NACIS (North American Cartographic Information Society)annual meeting in Sacramento, California, the goal is to give cartographers an off-the shelf solution for creating small-scale world, regional, and country maps. It has several features of interest to mountain cartographers producing small-scale physical maps: rendered shaded relief images and GIS labels for many mountain peaks, ranges, and other physical features. But perhaps more importantly, it includes other reference themes that fit that physical geography.

Natural Earth data builds on Tom Patterson’s Physical Map of the World presented at the 2008 ICA Mountain Cartography Workshop, Lenk, Switzerland. With NACIS backing, we have launched a new website, naturalearthdata.com, where you can download Natural Earth and updated versions of Natural Earth Raster imagery of Natural Earth I and II raster imagery in perfect registration with vector line work. Both political and physical features are included in Natural Earth data.

Natural Earth solves a problem that many cartographers face: finding vector data for making publication-quality small-scale maps. In a time when the web is awash in interactive maps and free, downloadable vector data, such as Digital Chart of the World and VMAP, mapmakers are forced to spend time sifting through a confusing tangle of poorly attributed data. Many mapmakers working under tight project deadlines must use manually digitalized bases instead.

Small-scale map datasets of the world do exist, but they have their problems. For example, most are crudely generalized—Chile’s fjords are a noisy mess, the Svalbard archipelago is a coalesced blob, and Hawaii has disappeared into the Pacific two million years ahead of schedule. They contain few data layers, usually only a coast and country polygons, which may not be in register. The lack of good small-scale map data is not surprising. Large mapping organizations that release public domain data, such as the US Geological Survey, are not mandated to create small-scale map data for a small user community that includes mapmaking shops, publishers, web mappers, academics, and students—in other words, typical mountain cartographers. Natural Earth fills this oft-overlooked but important niche.

(source)