title: Bigger marker size for plot using pcolormesh
body: <p>I am trying to create a color mesh plot but the data points and their corresponding colors appear too small.</p>
  
  <p>My script is:</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  from mpl_toolkits.basemap import Basemap, cm
  import matplotlib.pyplot as plt
  
  
  
  df = pd.read_csv('data.csv', usecols=[1,2,4])
  df = df.apply(pd.to_numeric)
  
  val_pivot_df = df.pivot(index='Latitude', columns='Longitude', values='Bin 1')
  
  lons = val_pivot_df.columns.astype(float)
  lats = val_pivot_df.index.astype(float)
  
  fig, ax = plt.subplots(1, figsize=(8,8))
  
  m = Basemap(projection='merc',
          llcrnrlat=df.dropna().min().Latitude-5
          , urcrnrlat=df.dropna().max().Latitude+5
          , llcrnrlon=df.dropna().min().Longitude-5
          , urcrnrlon=df.dropna().max().Longitude+5
          , resolution='i', area_thresh=10000
          )
  
  m.drawcoastlines()
  m.drawstates()
  m.drawcountries()
  m.fillcontinents(color='gray', lake_color='white')
  m.drawmapboundary(fill_color='0.3')
  
  x, y = np.meshgrid(lons,lats)
  px,py = m(x,y)
  data_values = val_pivot_df.values
  masked_data = np.ma.masked_invalid(data_values)
  cmap = plt.cm.viridis
  m.pcolormesh(px, py, masked_data, vmin=0, vmax=8000)
  m.colorbar()
  
  plt.show()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/NFi33.png" alt="Image produced here"></p>
  
  <p>I'm looking to get the markersize larger of each data point but I can't seem to find any documentation on how to do this for pcolormesh</p>