Rarely do you have evenlyspaced data across an entire geographic space. Here is a way to fill in the gaps.
R

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Transitioning Map, Part 1: Mapping Irregular Data with Interpolation in R

Interactive charts in R
Interactive charts in R are still soso, but if you don’t mind giving…

Tilegrams in R
Last month Pitch Interactive launched an online tool for tiled cartograms, or tilegrams…

Learning R Versus d3.js for Visualization
For those who work with R and d3.js, the differences between the two…

How to Visualize Proportions in R
There are many ways to show parts of a whole. Here are quick oneliners for the more common ones.

How to Make Beeswarm Plots in R to Show Distributions
Try the more elementbased approach instead of your traditional histogram or boxplot.

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How to Make Square Pie Charts in R
Instead of traditional pie charts that rely on angles and arc lengths to show parts of a whole, try this easiertoread version.

R in the data journalism workflow at FiveThirtyEight
R has found its way into a good number of news groups who…

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Annotating Charts in R
Let the data speak for itself they say. That doesn’t work a lot of the time, and when that happens, you need to explain.

5 Tips for Learning to Code for Visualization
Here are some tips to get you started, based on my own experiences with R, and more recently, the JavaScript library d3.js.

A Course for Visualizing Time Series Data in R
Learn to visualize temporal patterns in a couple of days.

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Drawing Lines and Segments in R
Show connections and changes over time with start and end points.

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Drawing Circles and Ellipses in R
Whether you use circles as visual encodings or as a way to highlight areas of a plot, there are functions at your disposal.

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Drawing Squares and Rectangles in R
R makes it easy to add squares and rectangles to your plots, but it gets a little tricky when you have a bunch to draw at once. The key is to break it down to the elements.

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Voronoi Diagram and Delaunay Triangulation in R
The
deldir
package by Rolf Turner makes the calculations and plotting straightforward, with a few lines of code. 
Comparing ggplot2 and R Base Graphics
Figure out which is best with a sidebyside comparison.

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Adding Legends in R
Make sure you explain your visual encodings so that others can interpret them.

Emergency room data in R
For my graphic on emergency room visits over time and the other on…

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How to Customize Axes in R
For presentation purposes, it can be useful to adjust the style of your axes and reference lines for readability. It’s all about the details.

R growth on StackOverflow reigns supreme
Joshua Kunst did a quick analysis on tag usage on StackOverflow, the question…