I was trying to get the TPM density plot of RNA-seq samples (Around 500+).

I used the geom_density and density() function. I found that density() and geom_density() is a kernel density estimation. I assume that in density curve area under the curve is 1 so all the values should be below one. But I am getting max density value for a specific sample as 851 which is way more than expected. Can the density estimation value be more than 1?

I used this code.

tpm <- ggplot(filtered_tpm, aes(x=TPM, by=sample_name)) +  
    geom_density(alpha=0.5,color="black",adjust = 0.5) +   
    scale_x_continuous(breaks = c(-1, 5, 10, 15, 20), limits = c(0.3, 20)) +   
    labs(title="TPM Distribution") +   
    theme(
    title = element_text(),
    axis.text = element_text(),
    axis.title = element_text(),
    axis.title.x = element_text(),
    axis.title.y = element_text(),
     panel.background = element_blank(),
     legend.position = "right"   ) 

get_max_density_tpm <- function(each_sample_data){  
each_sample_density <- density(each_sample_data$TPM)   
max_density <- max(each_sample_density$y)   
return (list(max_density=max_density)) }

tpm_density_df <- filtered_tpm[,get_max_density_tpm(.SD),keyby = .(sample_name)][order(max_density,decreasing = T)]