map_estimates_pngs: Maps PNGs
In bcgov/cccharts: Plot Climate Change Indicator Trends for British Columbia

Generates maps of climate indicator data as png files.

map_estimates_pngs(data = cccharts::precipitation, by = "Indicator",
  station = FALSE, nrow = NULL, map = cccharts::bc, width = 500L,
  height = 450L, ask = TRUE, dir = NULL, climits = NULL,
  clab = ylab_trend, labels = TRUE, low = getOption("cccharts.low"),
  mid = getOption("cccharts.mid"), high = getOption("cccharts.high"),
  insig = "white", bounds = c(0, 1, 0, 1),
  ecoprovinces = c("Coast and Mountains", "Georgia Depression",
  "Central Interior", "Southern Interior", "Southern Interior Mountains",
  "Sub-Boreal Interior", "Boreal Plains", "Taiga Plains",
  "Northern Boreal Mountains", "British Columbia"), prefix = "")

`data`	A data frame of the data to plot
`by`	A character vector of the factors to separate plots by.
`station`	A flag indicating whether the plot is for stations or ecoprovinces.
`nrow`	A count of the number of rows when facet wrapping.
`map`	A SpatialPolygonsDataFrame object.
`width`	A count of the png width in pixels.
`height`	A count of the png height in pixels.
`ask`	A flag indicating whether to ask before creating the directory
`dir`	A string of the directory to store the results in.
`climits`	A character vector of length two providing limits of the color scale.
`clab`	A function that takes the data and returns a string for the color legend label.
`labels`	A flag indicating wether to plot labels.
`low`	A string specifying the color for negative values.
`mid`	A string specifying the color for no change.
`high`	A string specifying the color for positive values.
`insig`	A string specifying the color for insignificant estimates.
`bounds`	A numeric vector of four values between 0 and 1 specifying the start and end of the x-axis bounding box and the start and end of the y-axis bounding box.
`ecoprovinces`	A character vector specifying the ecoprovince areas to include in the map.
`prefix`	A string specifying the prefix for file names.