SWMM Plot (Nature figure specification)

Part of Agentic SWMM: install the project first for the executable toolchain (aiswmm CLI, SWMM solver, MCP servers).

Every figure this skill renders follows the Nature journal figure specification, the project's standing figure standard. Source: <https://research-figure-guide.nature.com/figures/preparing-figures-our-specifications/>. The spec lives in exactly three places here, and the scripts hand-set nothing:

Scope note: these are print-publication rules for the data figures of a run. They are not meant for the HTML report chrome or the CLI itself.

Before calling plot: ask the user

When the user asks to plot, always ask these questions first before calling any plot tool:

1. Which entity? A specific node (junction / outfall), by name, or a specific link (conduit), by name?

• List 3-5 high-peak-flow candidates from the run's RPT Link Flow Summary so the user can pick.

1. Which attribute? Node options: Total_inflow, Depth_above_invert, Volume_stored_ponded, Flow_lost_flooding. Link options: Flow_rate, Velocity, Depth.
2. Time window? Default is the full simulation (24h). Offer to limit to a focus day or HH:MM-HH:MM window if peaks occur in a short period.

Do not silently pick defaults. The user needs control: different plots answer different questions (peak inspection vs continuity vs flooding).

What this skill renders

Inputs: rainfall TIMESERIES from the .inp (inline, FILE, or [RAINGAGES] FILE), flow series from the .out binary (via swmmtoolbox), geometry from the INP text or the SWMManywhere / SWMMCanada upstream layers.

Non-negotiables

Always do

• Start from apply_style(); size with figsize("single" | "double") or map_figsize(bounds); save with save_figure(fig, out_png). Never plt.rcParams.update, never tight_layout(), never bbox_inches="tight" (it silently changes the physical width and breaks the 89/183 mm rule).
• Axis lines and tick marks on every axis; ticks point outward; top/right spines off (the hydrograph's flow axis keeps its own right spine).
• Put the key above the panel (legend_outside), so it never sits on data.
• Label every axis with units: Rainfall depth (mm/5 min), Flow (m³/s), Easting (m, EPSG:32610), X (INP units) when the INP's unit is unknown.
• Keep the figure about the run: the hydrograph draws only the rainfall inside the reported period (a 30-year 5-min climate file is 3M bars otherwise).
• Prefer 89 mm; reach for 183 mm only when the content needs it.

Never do

• Background gridlines
• Drop shadows, 3D effects, gradients as decoration
• Patterns/hatching to distinguish categories; use solid colours
• Coloured text (series are bound to axes by the key, not by tinted labels)
• Red/green pairings, rainbow/jet colourmaps
• Overlapping text, or text over busy backgrounds (the study-area cartouche sits on a white box)
• A title inside the figure
• A raster-only figure: an orphan PNG is what gets submitted by mistake

Wong colour-blind-safe palette

Black first, then in this order. Roles in this skill are fixed so the figures of one run read as one set:

Continuous data (the DEM hillshade) uses a monotonic grey ramp; never jet.

Workflow

inspect_plot_options  ->  real rainfall series name + node/link ids
swmm-runner.run_swmm_inp  ->  model.inp + model.out
plot_run / map_run    ->  08_plot/<name>.png + 08_plot/<name>.pdf

Call inspect_plot_options first so plot_run gets real names instead of placeholders. If several nodes need a figure, call plot_run once per node with a different out_png; each call writes its own PDF twin.

Writing a new figure type inside this skill? Same three calls:

from plot_style import apply_style, figsize, save_figure, WONG
apply_style()
fig, ax = plt.subplots(figsize=figsize("single"), layout="constrained")
...
save_figure(fig, out_png)        # out.pdf + out.png, size-checked, default bbox

PDF vs PNG: which file is which

The submission file is the PDF (vector, live text). The PNG is a preview: it is what swmm-report embeds (it globs 08_plot/*.png), what chat and slides show, what gets pasted into a draft. Both share a stem, which is how a checker knows the PNG is a preview and not an orphan raster. --dpi only affects the PNG (default 450, the spec's minimum for images).

Verify before calling a figure done

The repository test tests/test_swmm_plot_nature_style.py pins the physical size (89 mm), TrueType-embedded text and the PDF twin. When the nature-figures skill is on the machine, its checker inspects any output directly:

python3 ~/.claude/skills/nature-figures/scripts/check_figure.py 08_plot/fig_O1_Total_inflow.pdf 08_plot/fig_O1_Total_inflow.png

MCP tools

This skill backs three LLM-facing tools. plot_rain_runoff_si is routed through the MCP server; inspect_plot_options and map_run are direct Python handlers in the tool registry (agentic_swmm/agent/tool_handlers/swmm_plot.py and swmm_map.py).

1. `inspect_plot_options`: inspect a run directory (or an explicit .inp / .out path) and return the available rainfall series names, node IDs, and node output attributes. Call this before plot_run so you can pass real names instead of placeholders. Required args: run_dir (or inp_path + out_file). Read-only; auto-approved under the QUICK permission profile.

1. `map_run`: render the network layout as PNG + PDF. Reads the INP from the run directory automatically; pass inp to override. Required arg: run_dir. Optional: out_png, dpi, no_subcatchments, no_vertices.

1. `plot_run` (proxies to plot_rain_runoff_si on the MCP server): create the paired rainfall + flow figure from a run directory. Required arg: run_dir. Supply either node or link (mutually exclusive) to select the lower panel. Optional: rain_ts, rain_kind, node_attr, out_png. Figures default into the run's canonical plot stage (08_plot/), which is where swmm-report looks for embeddable figures; a RELATIVE out_png is anchored there too (never the process working directory), while an absolute path is honored verbatim. Day-window cropping: pass focus_day (YYYY-MM-DD) to crop the axis to one calendar day; pass window_start and window_end (both HH:MM) to further narrow to a sub-day window; both require focus_day (the server rejects window_start/window_end without focus_day).

`mcp/swmm-plot/server.js` exposes one underlying tool:

1. `plot_rain_runoff_si`: low-level render call used by plot_run. Prefer plot_run (which accepts run_dir) over calling this directly.

• Args:
• inp (required): path to the SWMM .inp (the rainfall TIMESERIES is read from here).
• out (required): path to the SWMM .out binary.
• outPng (required): where to write the PNG; the PDF twin lands beside it and is returned as outPdf.
• rainTs (no usable default: the schema ships the self-documenting placeholder <rainfall-series-name>, which fails at render time if not replaced; always supply the actual series name from the .inp [TIMESERIES] section via inspect_plot_options): name of the rainfall TIMESERIES inside the .inp.
• rainKind (default "depth_mm_per_dt"): one of intensity_mm_per_hr, depth_mm_per_dt, cumulative_depth_mm.
• dtMin (default 5): timestep of the rainfall series in minutes.
• node (no usable default: the schema ships the self-documenting placeholder <outfall-or-junction>, which fails at render time if not replaced; always supply a real outfall or junction name via inspect_plot_options): node ID to plot from the .out.
• nodeAttr (default "Total_inflow"): which swmmtoolbox attribute (e.g. Total_inflow, Lateral_inflow, Flow_lost_flooding).
• link (optional): conduit id; when set, the lower panel plots the link's Flow_rate instead of a node attribute. Mutually exclusive with node.
• width (default "single"): single (89 mm) or double (183 mm).
• dpi (default 450): PNG preview resolution; the PDF is vector.
• focusDay (optional, YYYY-MM-DD): crop axis to a single day.
• windowStart / windowEnd (optional, HH:MM; only valid together with focusDay): sub-day time window within the focus day. Rejected with a clear error if used without focusDay.
• padHours (default 2): padding around the rainfall extent when no focusDay is given.

Known limitations

• Only one rainfall series is plotted at a time (rainTs is a single name); multi-gauge inputs need separate figures.
• Multi-node ensemble plots, exceedance curves and sensitivity scans belong to swmm-uncertainty / swmm-calibration, not here.