# Hi evrybody, I'm trying to overlay a scatter plot with a heatmap using Plots.jl bu

Hi evrybody, I’m trying to overlay a scatter plot with a heatmap using Plots.jl but I can’t figure it out how heatmap is oriented (or find much documentation on the plots.jl heatmap function).
The heat map seems turned by 90 degrees (or transposed, transposing the heat-value matrix seems to fix the issue). Maybe it fills row-wise from the top left corner while reading the array column-wise?
Here is an example showing the problem

``````n_points = 100
w = [4, 0.7, -2.3]
σ(a) = 1 / (1 + exp(-a))
x_data = randn(n_points)
y_data = randn(n_points)
y_data[1:n_points÷2] .+= 8
labels = [round(σ(p'*w)) for p in eachrow([ones(n_points) x_data y_data])]
plt = scatter(x_data, y_data, zcolor=labels)
xs = range(-4, 3, length=100)
ys = range(-4, 11, length=100)
grid = [[1, x, y] for x in xs, y in ys]
heat = [σ(p'*w) for p in grid]
heatmap!(plt, xs, ys, heat, alpha=0.5)
# this doesn't look right

# now transpose and it does
plt = scatter(x_data, y_data, zcolor=labels)
heatmap!(plt, xs, ys, transpose(heat), alpha=0.5)
``````

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(Original message ) (More Info)

Well, you’ve solved your question, but FWIW, the reasoning is that heatmap’s orientation was made to match precedence (matplotlib IIRC), so the first dimension is the y axis and the second dimension is the x axis. This way, for example, taking a heatmap of a 3×5 matrix, as in

``````julia> heatmap(randn(3,5))
``````

produces a 3×5 matrix-looing plot, i.e., something like

OP here.