CODEWITHSUNDEEP
pythonipythonholoviewsdatashadergeoviews
BozhiWang
BozhiWang

Reputation: 113

how can i change the size of points in my map in holoviews?

here is my code:

import holoviews as hv
import datashader as ds
import dask.dataframe as dd
import geoviews as gv
from cartopy import crs

from holoviews.operation.datashader import datashade

hv.extension('bokeh', width=95)

%opts RGB     [width=1200 height=682 xaxis=None yaxis=None show_grid=False bgcolor='black'] 
%opts Shape (fill_alpha=0 line_width=1.5) [apply_ranges=False tools=['tap']] 
%opts Points [apply_ranges=False ] WMTS (alpha=0.5)


color_key = {worda:'red',  wordb:'green'}
races     = {worda:worda, wordb:wordb}


color_points = hv.NdOverlay({races[k]: gv.Points([0,0], crs=crs.PlateCarree())(style=dict(color=v))
                             for k, v in color_key.items()})

census_points = hv.Points(df, kdims=['x', 'y'], vdims=['word'])

x_range, y_range = ((-13884029.0, -7453303.5), (2818291.5, 6335972.0)) # Continental USA

shade_defaults = dict(x_range=x_range, y_range=y_range, x_sampling=10, y_sampling=10, width=1200, height=682,
                      color_key=color_key, aggregator=ds.count_cat('word'),)
shaded = datashade(census_points, **shade_defaults)
shaded()

and the result looks like: enter image description here but I want the size of points more bigger, like this: enter image description here

How can I change my code for my goal? Thanks!

Upvotes: 1

Views: 3055

Answers (2)

Sander van den Oord
Sander van den Oord

Reputation: 12818

As answered by James A. Bednar, using dynspread() works to make points in your datashaded scatter plot larger.
Your code should look like this:

from holoviews.operation.datashader import datashade, dynspread

dynspread(datashade(your_holoviews_scatterplot))

This makes sure that points in your datashaded scatterplot take up more pixels on your screen.

dynspread() has some parameters to influence the size of the markers, see also:
Documentation on dynspread()

You could for example change the threshold parameter to get even larger markers, although it doesn't make the plot prettier. Threshold can hold values between 0 and 1. Threshold is a tuning parameter, with higher values giving more spreading.

dynspread(datashade(your_holoviews_scatterplot), threshold=1.0)

Upvotes: 2

James A. Bednar
James A. Bednar

Reputation: 3255

(Copied from the parallel Github issue https://github.com/ioam/holoviews/issues/2877#issuecomment-405158027.)

So far, datashader only includes infinitely small points and infinitely thin lines, which would be invisible if not for the non-zero width of a pixel in the image. Adding the ability of a point or line to have an extent is something we plan to add eventually, but for now, you have a couple of options:

  1. Decrease the resolution of your image, making each isolated pixel more visible.
  2. Add "from holoviews.operation.datashader import dynspread" (or "spread"), then use spreading to expand each pixel into the neighboring pixels. Mathematically, this is not the same as having a non-zero extent, but it's an approximation to it that's valid when points are far apart (as most of the ones above are). Both have parameters that you can change to choose just how big you want to make the dots.

Upvotes: 1

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