Movement on maps: Beyond the travel record

Look at this map.... Did you notice that there changes along the x axis? Minard_carte_figurative.jpg Charles Joseph Minard’s visualization of Napoleon’s Russian campaign of 1812, (Tufte, 1983)

Content

  • Definition and purpose of flow maps
  • Different types of flow maps (charts)
  • Cartographic design principles (suggestions and limitations)
  • Examples in real world data: Fluvial Engineering

Definition

It is a type of thematic map, with the main purpose of represent, with the purpose of representing movement. For some author (Dodge et al., 2008), is a kind of hybrid map: a base map with flow diagram.

Common characteristics in visual variables:

  • Shape: Dot and lines
  • Orientation, Size and Colour: Depends on the attribute of the data, weight and frequency

Types

  • Sankey Diagrams
  • Chords
  • Origin Destination (OD)- Flow maps
  • Streamlines, streaklines and Pathlines
In [11]:
# OD Matrix, available on https://plotly.com/python/lines-on-maps/
print('OD Dataset size {}'.format(df_flight_paths.shape))
df_flight_paths.head()

OD Dataset size (178, 8)
Out[11]:
start_lat start_lon end_lat end_lon airline airport1 airport2 cnt
0 32.895951 -97.037200 35.040222 -106.609194 AA DFW ABQ 444
1 41.979595 -87.904464 30.194533 -97.669872 AA ORD AUS 166
2 32.895951 -97.037200 41.938874 -72.683228 AA DFW BDL 162
3 18.439417 -66.001833 41.938874 -72.683228 AA SJU BDL 56
4 32.895951 -97.037200 33.562943 -86.753550 AA DFW BHM 168
In [3]:
fig.update_layout(title_text = 'Feb. 2011 American Airline flight paths<br>(Hover for airport names)',
    showlegend = False,
    geo = dict(scope = 'north america',
        projection_type = 'azimuthal equal area',
        showland = True,
        landcolor = 'rgb(243, 243, 243)',
        countrycolor = 'rgb(204, 204, 204)',
    ),
)
fig.show()

Vector Fields Visualization

  • Streamlines: Line which connects velocity vectors at an instance in time. It is like a snapshot.
  • Streakline: A curved line formed by a string of fluid particles which have passed through a certain point.
  • Pathlines: Also called particle tracking, it is a path which a fluid particle traces
In [58]:
fig = plt.figure(figsize=(15,5))
gs = gridspec.GridSpec(nrows=1, ncols=3)
#  Varying density along a streamline
ax0 = fig.add_subplot(gs[0, 0])
ax0.streamplot(X, Y, U, V, density=[0.5, 1])
ax0.set_title('Varying Density')
#  Varying line width along a streamline
ax1 = fig.add_subplot(gs[0, 1])
lw = 5*speed / speed.max()
ax1.streamplot(X, Y, U, V, density=0.6, color='k', linewidth=lw)
ax1.set_title('Varying Line Width')
# With a obstacle "Masking"
ax2 = fig.add_subplot(gs[0,2])
ax2.streamplot(X, Y, U, V, color='r')
ax2.set_title('Streamplot with Masking')
ax2.imshow(~mask, extent=(-w, w, -w, w), alpha=0.5,
          interpolation='nearest', cmap='gray', aspect='auto')
plt.show()

Suggestions and Limitations

based on Jenny et al., 2018 and Andrienko et al., 2008

  • Curved vs. straight lines: People prefer circular arcs for graphs drawings. Less likely to create ambiguous analyses
  • Arrows vs. tapered flows: There is no consensus on which is better, it depends on the amount of data and the importance of the destination for the map.
  • Flows between areas vs. flows between nodes: Was found that flows between clear nodes in OD instead of non amarked areas result in lower error rates.

Geometry design tips, available on Jenny et al., 2018) FlowMap_GeometrySpecification.jpg

Current limitations and methodologies available on Andrienko et al., 2008

Visual_Procceses.jpg

An Application in Fluvial Engineering

Groynes in fluvial erosion, image avaiable on Buczyńska et al., 2018 Groynes.jpg

In [46]:
%%html
<iframe src="https://aamontalvo.github.io/MagangueEsp2/index.html" width="900" height="800"></iframe>

References

  • Andrienko, G., Andrienko, N., Dykes, J., Fabrikant, S.I. & Wachowicz, M. (2008) Geovisualization of Dynamics, Movement and Change: Key Issues and Developing Approaches in Visualization Research. Information Visualization, 7(3-4), 173–180. Available from: https://doi.org/10.1057/ivs.2008.23.
  • Buczyńska, E., Szlauer-Łukaszewska, A., Czachorowski, S. & Buczyński, P. (2018) Human impact on large rivers: the influence of groynes of the River Oder on larval assemblages of caddisflies (Trichoptera). Hydrobiologia, 819(1), 177–195. Available from: https://doi.org/10.1007/s10750-018-3636-6.
  • Dodge, S., Weibel, R. & Lautenschütz, A.-K. (2008) Towards a taxonomy of movement patterns⁤ // Towards a taxonomy of movement patterns. Available from: https://journals.sagepub.com/doi/epdf/10.1057/PALGRAVE.IVS.9500182 [Accessed 20 March 2023].
  • Jenny, B., Stephen, D.M., Muehlenhaus, I., Marston, B.E., Sharma, R. & Zhang, E. et al. (2018) Design principles for origin-destination flow maps. Cartography and Geographic Information Science, 45(1), 62–75. Available from: https://doi.org/10.1080/15230406.2016.1262280.
  • Tufte, E. (1983) The visual display of quantitive information. Graphic Press.