# Geom.contour in Gadfly.jl - How to use it?
**URL:** https://discourse.julialang.org/t/geom-contour-in-gadfly-jl-how-to-use-it/60123
**Category:** Visualization
**Tags:** gadfly
**Created:** [April 27, 2021, 7:25pm UTC](https://discourse.julialang.org/t/geom-contour-in-gadfly-jl-how-to-use-it/60123 "2021-04-27T19:25:26Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Adam\_Fleischhacker](https://discourse.julialang.org/u/Adam_Fleischhacker)
#### Post date: [April 27, 2021, 7:25pm UTC](https://discourse.julialang.org/t/geom-contour-in-gadfly-jl-how-to-use-it/60123/1 "2021-04-27T19:25:27Z")
I am trying to draw iso-density contours on a plot. Yet, it seems I am drawing lines all over the place – as opposed to contours representing different iso-densities (plot should be top-view of a mountain). I tried point and function representations, but my plot is wonky either way. I am missing something fundamental, but am not sure what it is? Any help is appreciated. Thanks!
Here is code to reproduce one of my wonky plots:
```julia
using Distributions, Gadfly, Format, DataFrames
## specify random variables
X = Beta(2,2)
unscaledBeta = Beta(2,8)
Y = LocationScale(0, 100000, Beta(2,8))
## calculate log pdf
function negLogDensFun(x::Real,y::Real)
-logpdf(X,x) - logpdf(Y,y) ## logpdf built-in to Distributions
end
## test it
negLogDensFun(0.5,25000)
## sample directly and show on grid
numDraws = 100
plotDF = DataFrame(winningsMultiplier = rand(X,numDraws),
maxWinnings = rand(Y,numDraws))
plotDF.negLogDens = negLogDensFun.(plotDF.winningsMultiplier,
plotDF.maxWinnings)
# make plot
plot(plotDF, x = :winningsMultiplier,
y = :maxWinnings,
layer(Geom.point),
layer(z=(x,y) -> negLogDensFun(x,y),
Geom.contour(levels = 3)),
Coord.cartesian(xmin =0, xmax = 1,
ymin = 0, ymax = 10^5),
Scale.y_continuous(labels = x -> format(x, commas = true)))
```
Wonky plot (above), but I was hoping for contour lines akin to the ones shown in the gallery (below):
My plot would have just one mountain top though.
---
### Author:  [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)
#### Post date: [April 27, 2021, 11:14pm UTC](https://discourse.julialang.org/t/geom-contour-in-gadfly-jl-how-to-use-it/60123/2 "2021-04-27T23:14:52Z")
Have you checked [this post](https://discourse.julialang.org/t/way-to-make-contour-plot-from-3-vectors/20118/4)?
---
### Author:  [@Mattriks](https://discourse.julialang.org/u/Mattriks)
#### Post date: [April 28, 2021, 12:11am UTC](https://discourse.julialang.org/t/geom-contour-in-gadfly-jl-how-to-use-it/60123/3 "2021-04-28T00:11:03Z")
The above example should work (because `z` is a function), but the issue is the `Inf` values on the edges of the domain (which I assume cause a problem for [Contour.jl](https://github.com/JuliaGeometry/Contour.jl)).
```julia
plot(z=(x,y) -> negLogDensFun(x,y), Geom.contour(),
xmin=[0.001], xmax=[0.999], ymin=[0.001], ymax=[10^4.9],
Theme(line_width=3pt)
)
```
---
### Author:  [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)
#### Post date: [April 28, 2021, 11:23am UTC](https://discourse.julialang.org/t/geom-contour-in-gadfly-jl-how-to-use-it/60123/4 "2021-04-28T11:23:38Z")
When a function is provided how many points Gadfly computes in order to produce the contours?
Another way using a matrix may allow some extra user control on the plot:
```julia
x = plotDF.winningsMultiplier
y = plotDF.maxWinnings
x0, y0 = sort(x), sort(y)
z0 = [negLogDensFun(x,y) for x in x0, y in y0]
Gadfly.plot( layer(z=z0, x=x0, y=y0, Geom.contour(levels=5)),
layer(x=x, y=y) )
```
---
### Author:  [@Adam\_Fleischhacker](https://discourse.julialang.org/u/Adam_Fleischhacker)
#### Post date: [April 28, 2021, 2:03pm UTC](https://discourse.julialang.org/t/geom-contour-in-gadfly-jl-how-to-use-it/60123/5 "2021-04-28T14:03:47Z")
> [@Mattriks](#):
>
> ```julia
> plot(z=(x,y) -> negLogDensFun(x,y), Geom.contour(),
> xmin=[0.001], xmax=[0.999], ymin=[0.001], ymax=[10^4.9],
> Theme(line_width=3pt)
> )
>
> ```
Thanks for this tip. I was missing the sort step when I tried going the matrix route.
---
### Author:  [@Adam\_Fleischhacker](https://discourse.julialang.org/u/Adam_Fleischhacker)
#### Post date: [April 28, 2021, 2:06pm UTC](https://discourse.julialang.org/t/geom-contour-in-gadfly-jl-how-to-use-it/60123/6 "2021-04-28T14:06:39Z")
This is fabulous. Thank you for debugging this - I was out of ideas and very much appreciate the support 🙂