Submitted by email:

Looking at your geocoding tutorial, you really should reference the Google terms of service (https://developers.google.com/maps/terms). They are quite restrictive; in particular sections 10.4.d & e require use of their data only in their maps. So it is a violation of their terms of service to use their API to geocode addresses for use in any other map.

You might want to refer readers to less-restrictive geocoding services. Personally I use the Texas A&M service but it is US only:
http://geoservices.tamu.edu/Services/Geocode/

This looks promising for world-wide geocoding though I have not tried it:
http://geocoder.opencagedata.com/

Other possibilities are listed here:
http://geoservices.tamu.edu/Services/Geocode/OtherGeocoders/
http://www.programmableweb.com/news/7-free-geocoding-apis-google-bing-yahoo-and-mapquest/2012/06/21

Re: accuracy / R APIs from emailer:

I don't have information on accuracy and I don't know of R API's. The Texas A&M has quite a bit of technical information available at http://geoservices.tamu.edu/Services/Geocode/About/. It has a simple web API and can return results as CSV data so parsing in R should be pretty simple. I have always used their batch service, uploading a CSV file and getting the results back as CSV to use for mapping.

As pointed out by @edzer , don't really need to introduce users to @ notation, or @data notation. Was required when I thought was required for attribute joins, but can now be removed.

Hi Nick,

I found an error using geocode function:

locations <- geocode(addresses, source = "google", output = "more")
Error in geocode(addresses, source = "google", output = "more") :
unused argument (source = "google")
but, when I run it without source parameter, it works well:
geocode(addresses)
What could be wrong here?

A little suggestion to your tutorial 4, you can use this:

addresses <- read.csv("C:/RGIS4_Data/addresses_to_geocode.csv", stringsAsFactors = FALSE),
to avoid one line in your code,
addresses <- read.csv("RGIS4_Data/addresses_to_geocode.csv")
addresses$Location <- as.character(addresses$Location)

Thanks for your tutorial, it is really good.

Jaime