War Room: terrain, communications and hazard methods

Return to the map · Method version war-room-terrain-v1

The map separates source observations and official advisories from local terrain-derived screening models. A reference point is not an impact footprint; an absence of records or shading does not establish safety. No overall disaster probability or universal “safe site” score is calculated.

Terrain analysis

Pick a site or use the map center, then select Analyze area. Change the display to slope, aspect, drainage, low ground, visibility or an elevation-threshold scenario. Fit study area frames the result. Candidate details offer Analyze from this candidate. Shift-click lets you inspect underlying reference features while an analysis overlay is present.

Choose a study site or the map center and a width of 2–40 km. The browser samples a 41×41 grid from Mapzen Terrarium composite elevation tiles. A 10 km study uses 250 m grid spacing. Tile zoom is adapted to the sample spacing; tile pixel spacing is not a guarantee of the underlying DEM resolution or accuracy. The outer sample ring supports derivatives and is not rendered as full analysis cells. At least 90% valid elevation samples are required. Missing pixels are never replaced with zero.

Layer/tool	Method and interpretation
Slope and aspect	Centered finite differences estimate slope and downhill compass aspect. They describe the sampled surface, not survey-grade parcel gradients. Flat terrain has no defined aspect.
Contours	Marching-squares interpolation of the sampled grid. The requested 10–1,000 m interval is coarsened if needed to limit the number of levels; the effective interval is reported. Up to 10,000 segments are displayed. These are derived contours, not surveyed lines.
Relative low ground	Cells at or below the study grid's lower elevation quartile. Ties can include more than one quarter of the cells. This relative comparison is not a mapped floodplain or flood probability.
Drainage / wetness proxy	Unfilled D8 routing sends each sample to its steepest lower neighbor. Accumulation follows descending elevations. The displayed proxy is ln(contributing cells × grid spacing / max(0.01, steepest downhill gradient)). It is sensitive to resolution, depressions, DEM noise and the study boundary. Upstream areas outside the grid are omitted. Rainfall, soils, infiltration, drainage works and levees are not modeled. The proxy is not applicable over open water and is not calibrated flood susceptibility.
Elevation threshold scenario	Highlights DEM elevations at or below the chosen number of metres in the DEM's vertical reference. Existing water and disconnected basins can be included. This is not a water-depth calculation, levee-breach model, sea-level projection or hydrodynamic inundation forecast.
Higher-ground candidates	Positive-elevation local maxima in the upper elevation decile, with positive local relief and spatial separation. At most 12 are returned. Candidate slope uses the greater of the local gradient and steepest neighboring downslope angle. Land/water classification, ownership, access, foundations, vegetation, weather exposure and site suitability are not established. Below-datum dry land is excluded by this conservative positive-elevation candidate rule.
Terrain visibility	Sampled rays from the central observer to receiver-height grid locations, using interpolated grid elevations and a 4/3 effective Earth radius. Green means terrain-clear within this coarse model; red indicates a sampled obstruction; unknown data remains unknown. Buildings, trees, sub-grid ridges and varying atmospheric refraction are not modeled.

Two-point communications profile

Choose endpoints 20 m–50 km apart. The browser samples 129 equally spaced points along the short great-circle path. Observer height is 1–150 m above sampled ground; receiver height is 0–150 m. For frequency 30–6,000 MHz, the first Fresnel radius is sqrt(wavelength × d1 × d2 / total distance). Effective-Earth curvature bulge is d1 × d2 / (2 × (4/3) × Earth radius). The profile reports minimum terrain clearance and minimum clearance after reserving 60% of the first Fresnel radius, over interior samples.

This is a terrain-clearance screen, not a link budget or radio-coverage prediction. It omits buildings, canopy, antenna patterns and polarization, transmit power, receiver sensitivity, interference, diffraction/fading and variable refraction. A narrow obstruction between samples can be missed. Frequency affects the Fresnel calculation, not the area terrain-visibility layer. The chart shows sampled elevation and the straight endpoint-height line; curvature and Fresnel margins are separately reported numerically. The displayed profile path is not a road or travel route.

Antenna planner and nearby-site comparison

Open Antenna planner in the top tool bar. Pick A and B yourself, use the map center, enter coordinates, or drag the labeled markers. Select Calculate link & heights. The planner samples 257 equally spaced points along the short great-circle path, for links 20 m–50 km long. It accepts 0–300 m antenna heights above sampled ground, 30–6,000 MHz frequency, 0–100% first-Fresnel clearance, a 0–100 m extra clearance allowance, and an effective Earth-radius factor between 2/3 and 2. The normal screening selection is 4/3. Profile/grid sample spacing and nominal decoded tile-pixel spacing are reported separately: oversampling does not increase the underlying DEM resolution or vertical accuracy.

For path fraction t, every interior terrain sample imposes the inequality (1−t)hA + t hB ≥ terrain + curvature + Fresnel reserve + extra allowance − interpolated endpoint ground. Fixed-endpoint options solve these inequalities directly; the equal-rise option raises both antennas by the largest deficit. A convex, two-variable height search minimizes combined antenna height within the chosen limit. Recommendations round upward to 0.1 m. The limit is a user search constraint, not an assessment of structural feasibility. Height suggestions can be applied and recalculated without fetching the same terrain again.

Find better nearby points tests the original position plus eight evenly spaced positions on the selected 50–2,000 m radius around each movable endpoint. You may hold A or B fixed. At most 81 pairs are screened, each with 129 terrain samples. Paths with missing terrain are excluded. Feasible pairs rank by lowest combined required antenna height, with shorter relocation breaking ties. These are the best of the sampled alternatives, not a global optimum or a land-use/ownership/access assessment. Narrow ridges, buildings and trees can be missed; extra clearance is an explicit assumption, not a measured canopy model. The profile distinguishes curvature-adjusted terrain, the antenna line and its Fresnel/extra-clearance boundary.

Hypothetical dam-release scenario creator

Open Dam scenarios, name the scenario, and put A at the downstream toe of the dam and B at a lower point farther down the valley. A loaded Wikidata dam/reservoir reference can provide a starting point, but its coordinate can be a reservoir or structure centroid: adjust it to the downstream toe. The selected points define a 0.2–30 km long, 0.5–20 km wide oriented study, sampled on a 65×41 grid. Source coverage must be at least 95%, with valid endpoint elevations.

This is a transparent terrain-connected, assumed-stage screening scenario, not a hydrodynamic dam-breach simulation. The form does not infer a dam's breach probability, released volume, failure mechanism or reservoir operating state from a reference point. Defaults are illustrative user assumptions. No wave arrival time, velocity, structural damage, fatalities or safe evacuation route is predicted.

The user supplies a stage rise above the sampled near-toe ground and a far-end rise. Far-end ground must be lower than near-toe ground, and the far-end rise cannot exceed the near-toe rise. Stage rise is not dam height or reservoir depth.
A straight water-surface profile joins the two endpoint ground elevations plus their assumed rises. The same surface elevation is applied across each lateral grid row; this is an imposed scenario surface, not a solved free surface.
Starting at the toe cell, four-neighbor connectivity includes cells whose sampled ground is below that scenario surface. Cells behind an above-surface barrier remain disconnected. Diagonal corner jumps are not permitted. Missing terrain is unknown and blocks propagation, so downstream continuation can be omitted.
Lower, central and higher sensitivity variants multiply both user rises by 0.5, 1 and 1.5. These factors are not confidence intervals, occurrence probabilities or forecasts. The map colors the earliest variant containing a cell: blue lower, amber central-only, rose higher-only. Grey marks unknown terrain.
An optional released-volume budget limits the sum of positive scenario depth proxies × connected cell area. If needed, bisection reduces the rise multiplier to remain within this static storage budget. It does not account for moving water or calculate a breach discharge hydrograph. A disconnected basin may require more volume than the budget before its modeled connection opens; in that case it can remain unhighlighted.
The near-source/upstream edge ends at the selected toe; the reservoir is not modeled. Side and far-end boundary contact is reported as clipping, not proof of a complete flood extent. The depth proxy is scenario surface minus sampled DEM, not measured or calibrated water depth. No land/water mask or initial-water-level model is applied, so existing water and below-datum terrain can be included in cells and storage; those areas are not necessarily newly flooded land.

Open Check a village, bridge or other place to add named points. The report compares those points and currently loaded dam/reservoir, port and resource references with the scenario cells. This is a bounded point inventory, not complete coverage of buildings, roads, population, affected households or casualties. Outside-study and unknown-terrain locations are unevaluated; an unhighlighted point is not established safe. Basemap roads and settlements provide visual context, not a counted exposure inventory.

Up to five results can be saved for comparison within the current page session. Export result downloads GeoJSON with the original input locations and assumptions, sampling metadata, scenario variants, exposure summary and method limitations. Load scenario inputs accepts those inputs, then requires recalculation; imported result claims are not applied as verified analysis. Nothing is automatically published or stored in a server-side scenario account.

For an actual dam-safety study, an appropriate hydraulic workflow includes surveyed terrain/bathymetry, reservoir level/storage, dam geometry, breach formation and hydrograph assumptions, channel roughness, structures, boundary conditions and calibration. See the USACE HEC-RAS dam/levee breach documentation. The local screen here is useful for exploring assumptions and identifying places for further review, and is not a replacement for that workflow.

Hazard and warning layers

Layers reuse Watchtower's public Natural Hazards Command and terrestrial-weather collections: USGS earthquakes, NASA FIRMS/EONET, NOAA/NHC, GDACS and named national or CAP issuing authorities. Their coverage is source-bounded and uneven. Tornado, severe-weather and other warning coverage follows participating issuing authorities; it is not a complete worldwide warning system.

Warning/advisory polygons are areas covered by the issuing product, not necessarily observed impact extents. No impact radius, storm track or inundation polygon is manufactured from an event point.
USGS tsunami flags are follow-up context attached to earthquake epicenters, not official tsunami warnings or wave observations.
Thermal-anomaly centroids are not confirmed wildfire causes, burned areas or perimeters.
Expired warnings are removed. Future-dated official products can appear as upcoming source times; future-dated observations are excluded. Source issue/effective-time conventions vary.
Older or source-stale events are hidden unless history is enabled. Fire observations use a three-day screening window, official products without expiry a seven-day window, and other event records up to fourteen days. These windows do not establish that an event has ended.
Missing/invalid geometry and zero-coordinate placeholders are not converted into guessed locations. Dated alerts without usable geometry remain in the unmapped-alert list.
Each source refreshes independently. Cached records keep their original dates; a failed refresh is shown explicitly. References can be temporarily unavailable if an upstream service fails.

Regional reference overlays

Global satellite context: NASA EOSDIS GIBS serves the IMERG_Precipitation_Rate daily precipitation-rate imagery and VIIRS_Combined_Flood_3-Day classification (NOAA-20 + NOAA-21 VIIRS). The date selector defaults to the previous UTC day and is bounded to the preceding 90 days. Precipitation is a satellite estimate, not ground radar or a forecast. The flood product is a three-day satellite classification, not ground-confirmed water depth or guaranteed cloud-free flood coverage. Product gaps, cloud effects, permanent-water classification and publication lag apply. Blank or transparent pixels do not establish no flooding or rain. Raster colors retain the source's product symbology; they are not the DEM threshold scenario. NASA GIBS documentation and NASA Worldview source legends. Raster pixels are not included in GeoJSON exports; selected products and dates are recorded.

U.S. Drought Monitor: the weekly D0–D4 raster covers the United States only, from NDMC / USDA / NOAA. Optional GDACS drought points provide sparse global impact context, not a continuous global severity surface.

U.S. fault references: the USGS Quaternary Faults service labels itself “2020 Release.” It provides geological reference traces/areas for the United States, not global active-fault completeness or current earthquake probabilities. Service and source legend.

Site brief and infrastructure context

The brief reports whether the study point lies inside selected source warning/advisory polygons and shows nearby point events as distance context. Distances are not impact radii. Loaded dam/reservoir, port and resource reference points can be compared with warning polygons; their presence inside a warning area does not confirm damage, outage, exposure of an entire facility or a safe evacuation route. Only loaded references are reviewed, and the list is bounded.

Export and reproducibility

GeoJSON exports carry source dates on hazard records, the analysis time, grid spacing, study center/width, contour interval/cap, observer/receiver parameters and profile assumptions. Analysis generation time is not the date of an elevation survey. Changed form values do not silently change retained output: rerun the analysis or profile to apply them. Source data and modeled outputs must retain their separate meanings when reused.

Terrain attribution

Terrain Tiles was accessed from the Registry of Open Data on AWS. Mapzen/Terrain Tiles is a source mosaic. Local source dates, resolution, vertical reference and accuracy vary. See provider attribution and data-source details. Analysis transforms sampled elevations; source providers do not endorse these derived models.

ArcticDEM terrain data DEM(s) were created from DigitalGlobe, Inc., imagery and funded under National Science Foundation awards 1043681, 1559691, and 1542736.
Canada terrain data contains information licensed under the Open Government Licence – Canada.
Europe terrain data produced using Copernicus data and information funded by the European Union – EU-DEM layers.
Global ETOPO1 terrain data: U.S. National Oceanic and Atmospheric Administration; DOC/NOAA/NESDIS/NCEI, National Centers for Environmental Information. Bathymetry is not a navigation sounding.
Mexico terrain data source: INEGI, Continental relief, 2016.
United States 3DEP (formerly NED), global GMTED2010 and SRTM terrain data courtesy of the U.S. Geological Survey.

Other base/reference layers retain their existing attribution: OpenFreeMap / OpenMapTiles / OpenStreetMap (ODbL), Natural Earth, GLOBathy, Wikidata, Esri imagery, UN Global Platform / IMF PortWatch, and named Commodity Atlas sources.