Sitemaps uses a set of custom functions and a few key functions from other R packages. The descriptions are minimal here. The following chapters provide a more in-depth discussion, along with examples, of the functions.
Custom Functions
All of these functions work in conjunction with data and other tables. The functions assume that standard column names are being used1.
For convenience, each of these functions begins with “site_” and most end with a plural suffix.
site_cuts: Divides quantitative data in a column into index values based on segmentation. There are a number of segmentation strategies. This is useful when you want to use a few colors to represent the data, such as elevation ranges or response values.
site_elevations: Obtains the elevations for a set of locations. This uses the Google Maps API.
site_fans: This function generates a special “fan shaped” symbol. The symbol show a direction and distance. This is useful for showing photo locations.
site_google_basemap: This function creates basemaps using the Google Map services. The location and size of the basemap is determined by the (lat, lon) in your datatable. You can specify the type of map and suppress information layers.
site_hides: The hide values are downloaded with this function. They will be used to suppress layer information when basemaps come from Google Maps.
site_labels: The data in the names_table are used to add text labels to data locations (lat, lon). There are many style specifications that can be used with values either as table columns (when labels have different styles) or as a param value (for a constant style for all labels).
site_legend: This is a rather complex function that builds lines with text or symbols and text. Use these lines to create a custom legend for a map.
site_names: The names_table has text, location and style information for a names overlay applied to a basemap. Like points and labels, the style descriptions are either in table columns or used as param.
site_photos: Photo EXIF data are retrieved with this function. This includes the geographic coordinates, file name, description, date and time.
site_points: The datatable locations (lat, lon) are used to create a point layer for use with a basemap. Columns can be used to specify style features. There are a number of param that also control point styles.
site_scale: Places a scale bar and text message in one of the four corners of a map. A number of parameters are available to control the appearance of the scale information.
site_squaremaps: Used to make a Stamen basemap square. This corresponds to Google basemaps that are always square.
site_stamen_basemap: Creates a Stamen basemap by using the location and extent of the geographic coordinates in the datatable. Options include the map type.
site_styles: This function downloads the default parameters for points, labels, names and a few other useful values.
site_textwraps: Wraps the character strings in a text column by inserting “\n” into the string. The value in the wrap column determines the maximum string length. Strings are broken at spaces so words are not divided. A column value of NA means to not break the string. Note that this is done more often using column specifications in data tables (label_text_wrap, name_text_wrap) or the equivalent column parameters (column\(label_text_wrap, column\)name_text_wrap).
site_legend: Provides a simple toolkit using two tables to create a map legend. This is quite flexible and scales from simple to complex legends.
Other Key Functions
These functions come from the ggmap, ggplot2, and gt packages.
register_google: This function is used once each day to link your Google Map Key to your use of the Google Map services.
get_googlemap: Retrieves a Google basemap when you provide a central location, zoom level and maptype. The location can be a placename or geographic coordinates. You can also selectively suppress information layers.
get_stamenmap: Retrieves a Stamen basemap. You provide a bounding box (left, bottom, right, top), zoom level and maptype. You can get the bounding box from a placename by using the geocode function.
geocode: A Google Maps service that uses a place name to retrieve geographic coordinates.
ggmap: Plots a basemap (either Google or Stamen) with layers for points, labels and names. There is considerable control over the appearance as the ggplot2 functions can generally be applied, such as a theme.
gt: This function prints tables. You can enhance the table with a caption and footnotes.
A number of other functions, primarily associated with data manipulation, are also used.
Footnotes
Yes, I know this is not the way things are usually done in R, but this requirement goes a long way in making the map-creation process accessible to novice programmers.↩︎