ggplot Discrete Legend Continuous Data - r

Question

I'm new to R programming but I'm enjoying the challenge of writing code!
I created a GIF by stitching multiple map plots together. Unfortunately,
my legend is referencing the particular year of the map being generated and as a result, the GIF shows a legend that has its marks moving up and down. I think the solution would be to have the legend reference the entire data-frame rather than the given year. How do I do this?
Link to the GIF:
https://1drv.ms/i/s!Ap-NxMqZOClHqgsFHSxo-kR1pLrr
##This is the R-Code I used for the year 1950:
kansas1950 <- readShapePoly("KansasCOUNTIES.shp")
## Kansas Winter-Wheat Planted from Quickstats
kansas1950.acres <- read.csv(file = "KWW 19502016 QuickStatsEst.csv",
stringsAsFactors = FALSE)
## Create a smaller dataset by retaining the kansas Acres in 1950 and the FIPS
## FIPS, which will be used for matching and merging with the input shapefile
smaller.data1950 <- data.frame(FIPS = kansas1950.acres$FIPS, Acres = kansas1950.acres$X1950)
smaller.data1950 <- na.omit(smaller.data1950)
## Join the two datasets using their common field
matched.indices1950 <- match(kansas1950#data[, "FIPS"], smaller.data1950[, "FIPS"])
kansas1950#data <- data.frame(kansas1950#data, smaller.data1950[matched.indices1950, ])
## Compute the cartogram transformation of each county using its population
## with the degree of Gaussian blur = 0.5
kansas1950.carto <- quick.carto(kansas1950, kansas1950#data$Acres, blur = 0.5)
## Convert the object into data frame
kansas1950.carto <- gBuffer(kansas1950.carto, byid=TRUE, width=0)
kansas1950.f <- fortify(kansas1950.carto, region = "FIPS")
## Merge the cartogram transformation with the kansas map shapefile
kansas1950.f <- merge(kansas1950.f, kansas1950#data, by.x = "id", by.y = "FIPS")
# Plot of the transformed polygons, where each county is
## further shaded by their acreage (lighter means bigger)
my_map1950 <- ggplot(kansas1950.f, aes(long, lat, group = group,
fill = kansas1950.f$Acres)) + geom_polygon() +
scale_fill_continuous(breaks = c(0, 10000, 100000, 200000, 526000),
labels = c("0 Acres","10k Acres", "100k Acres", "200k Acres", "526k Acres"),
low = "black",
high = "purple"
) +
labs(x=NULL, y=NULL) + labs(fill = "Acres Planted")
# Remove default ggplot layers
my_map1950 <-my_map1950 + theme_bw() + theme(panel.border = element_blank(), panel.grid.major = element_blank(),
panel.grid.minor = element_blank(), axis.ticks=element_blank(),
axis.text.x=element_blank(),axis.text.y=element_blank(),
axis.line = element_line(colour = NA))
# Citation
my_map1950 <- my_map1950 + labs(caption = "USDA-NASS Quick Stats") + ggtitle("1950 Kansas Winter-Wheat Acres Planted")
my_map1950
# Save a higher resolution PNG
png('my_map1950kwwpurp.png', units="in", width=10, height=8, res=300)
my_map1950
dev.off()

Answer 1

Assuming this is what you want, try adding this to your plot (but, of course, specifying your own custom lower and upper limits):
+ scale_fill_gradient(limits = c(0, 10))
I have a sample df that worked:
df <- data.frame(x = 1:10)
p <- ggplot(df, aes(x, 1)) + geom_tile(aes(fill = x), colour = "white")
p + scale_fill_gradient(limits = c(0, 10))
p + scale_fill_gradient(limits = c(0, 20))
Here's the graph with the scale set from 0 to 10.
Here's the graph with the scale set from 0 to 20.
EDIT: Oh, I see now that you have called scale_fill_continuous() in your code. Try adding a limits argument similar to what I did to that.