Shreyas Gadgin Matha

Answered few more questions in FAQs.md

export_png() should not require external program to save as png

5

`export_png()` requires vega to be installed. This should be a feature that is built into ggvis, especially because so many users ([1](http://stackoverflow.com/questions/25999741/getting-ggvisexport-png-working), [2](http://stackoverflow.com/questions/27002277/ggvisexport-png-on-windows), [3](http://stackoverflow.com/questions/29035628/how-to-save-a-ggvis-plot-displayed-in-the-viewer-panel-of-rstudio-with-an-r-scri)) have faced difficulties in installing vg2png...

When axis labels are rotated, ggvis should automatically move the axis title to avoid overlaps with labels. This is what we would want: ``` ggplot(iris, aes(x = Species,y = Sepal.Length))...

Simple port to Python 3

Minor documentation issue in `blackmarble.raster.bm_raster`

1

## Bug Report ### Description `blackmarble.raster.bm_raster` takes parameter `gdf`, but the API reference mentions `roi` instead. #### Screenshots / Error Messages (if applicable) 

RPOP - Handling zeros in diversity / ubiquity

2

Diversity / ubiquity is often 0 when calculating with RPOP. Need better handling of these cases, since ECI / PCI show up as NaN for all countries in these cases...

Added comments to briefly explain why PCI values are not normalized with PCI mean and std deviation.