How to plot points on Indian map by using R Language

I started creating Maps through R. There are number of packages to take care of this. In this post I shall explain as how to fetch map with the help of  "ggmap" and then plot it with "ggplot2". 

We need a data file consisting coordinates (longitudes, latitudes) of any given terrain. In this post I am going to explain plotting points on Indian map. So, the steps are going to be: 

1. Preparing a data file with logitudes and latitudes
2. Fetching map from google server
3. Plotting points on the server

Step - 1: Preparing a data file with logitudes and latitudes: 

I already prepared a file which consists of coordinates and also a data column of accidents in different cities in India. You can download the file from here.  The data file is basically a CSV (comma separated values) file. It is easy to import CSV file in R (you may also import Excel files but it is not strait).  The following is the procedure to import the (CSV) file.

> my.df <- file.choose="" font="" read.csv="">
> my.df

my,df is my data set (which is basically an object) in which there is data column (variable) "accidents".  You may look at the variables (columns) by executing the following command in R editor. 

> edit(my.df)

Step - 2:  Fetching map from google server

The following procedure illustrate as how to get Indian map from google server. We need two packages I am going to invoke the libraries by using command "library"

> library(ggmap)
> library(ggplot2)
> my.map <- get_map="" india="" zoom="5)</span">
> ggmap(my.map)

You can see Indian map popping up in graph canvas adjacent to R console. The following is the graph retrieved from google server.        

Step - 3: Plotting points on the server

Now we are going to identify those cities (listed in our data file) where the accidents are identified. 

> ggmap(my.map)+geom_point(data=my.df, aes(x=my.df$Longitude, y=my.df$Latitude, label=my.df$acci))

We get the following map. 

But the points are not distinct, so let me make them little better by changing the color (red) and size (3.5).

> ggmap(my.map)+geom_point(data=my.df, aes(x=my.df$Longitude, y=my.df$Latitude, label=my.df$acci), color="red", size=3.5, alpha = 0.5)

The following is the map that I get with the help of above statement.

Now I guess it is better to get number of accidents just adjacent to the point. Isn't it? I can get the numbers just adjacent to the point by following statement.

> ggmap(my.map)+geom_point(data=my.df, aes(x=my.df$Longitude, y=my.df$Latitude, label=my.df$acci), color="red")+geom_text(data = my.df, aes(x = my.df$Longitude, y = my.df$Latitude, label = my.df$acci), size=3.5, vjust = 0.5, hjust = -0.75)

The following is the map that we can produce with above statement.

I hope you got the point!

How is it? Now, I am going to give you assignment! Yes, exactly.....
Delete the numbers and try to draw draw a line between any two given points on this map. You can also try on satellite map rather than a terrain map.

All the best!