Data sources and licenses

MitchellCo uses this page to provide more source, license, provenance and attribution information than can reasonably fit inside a map control. This is an operational publication record, not legal advice. Source terms can change, so links below point to the source organizations' current guidance.

Publication policy

MitchellCo public maps fail closed on source permissions: sources classified as blocked, needing clearance, unknown, or unreviewed are not intentionally published. Derived scores and interpretations are MitchellCo products, not products or endorsements of the underlying data providers. MitchellCo does not use NASA, NOAA/NWS, Census, or other government logos as site branding. Read the Earthdata EULA publication policy.

Reuse of MitchellCo maps

TL;DR: Use and redistribute these maps freely, including commercially, but you remain responsible for complying with every underlying data-source license and attribution requirement.

Unless otherwise noted, MitchellCo-authored software in this project, including HTML, CSS, JavaScript and Python, is licensed under the MIT License. MitchellCo-authored documentation, explanatory prose and original non-software SVG artwork are licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).

When redistributing or adapting a map, retain the MIT copyright and permission notice for MitchellCo software and provide the attribution required by CC BY 4.0 for MitchellCo-authored documentation and artwork. These licenses do not relicense third-party data, imagery, map tiles, software, trademarks, logos or other materials. Those remain subject to the source-specific licenses, EULAs, attribution requirements and terms listed on this page. A third-party layer may need to be removed or replaced if its terms do not permit your intended use.

Map 25 · Watershed Explorer

U.S. Geological Survey · Network Linked Data Index / NHDPlusV2

Hydrologic network connectivity

Watershed Explorer uses the USGS Network Linked Data Index (NLDI) to locate a NHDPlusV2 reach for a clicked coordinate and retrieve bounded upstream and downstream flowline navigation. The map always supplies an explicit navigation distance and does not request the service's very large implicit default.

Reuse: USGS-authored or produced data and information are considered public domain in the United States. MitchellCo retains explicit USGS source credit. This map does not use the USGS logo or imply USGS endorsement.

Interpretation: The displayed traces are NHDPlusV2 network connectivity. They do not estimate contaminant travel time, current discharge, flood stage, or whether water is presently flowing through every displayed reach.

Map 26 · Dark Sky Tonight

U.S. Census Bureau · 2025 Gazetteer and Vintage 2025 population estimates

Candidate place names, coordinates and selection population

The 100-place ranking uses official 2025 Census Gazetteer place names and representative latitude/longitude coordinates. Candidate selection uses the Census Bureau Population Estimates Program Vintage 2025 national subcounty file and its July 1, 2025 POPESTIMATE2025 field to identify a highest-population incorporated place and, where a distinct one is available, a low-density incorporated place in each contiguous state/DC. Population is used to construct the representative candidate set, not as an ingredient in the Tonight Score.

The ranking covers only these 100 representative Census places. It does not claim to rank every location or observing site in the United States, and no Census Bureau endorsement is implied.

NASA VIIRS Black Marble annual imagery, 2016

Rendered reference imagery

Visible map credit: NASA Worldview / GIBS · Suomi NPP/VIIRS via NASA Earth Observatory · Black Marble 2016.

The map's historical nighttime-light overlay is delivered through NASA's Global Imagery Browse Services (GIBS). NASA Worldview identifies the layer as Black Marble - Nighttime Lights only (Annual, 2012 & 2016) from Suomi NPP/VIIRS via NASA Earth Observatory. MitchellCo uses the 2016 layer as historical visual context, not as a current sky-brightness measurement.

Non-endorsement: NASA does not endorse MitchellCo, this map, or the MitchellCo viewing score. No NASA insignia, logotype or seal is used as MitchellCo branding. NASA-hosted third-party copyrighted material, if specifically marked as such, is not treated as covered by NASA's general imagery guidance.

NASA VIIRS VNP46A4 Collection 2, 2024

Scientific radiance data

The ranking prototype uses the 2024 annual VNP46A4 Collection 2 product at build time. The Earthdata token used to access LAADS is a private build credential and is not included in public HTML, JavaScript or JSON.

Dataset citation supplied for the product:
NASA VIIRS Land Science Investigator-led Processing System. (2025). VIIRS/NPP Lunar BRDF-Adjusted Nighttime Lights Yearly L3 Global 15 arc second Linear Lat Lon Grid [Dataset]. NASA Level 1 and Atmosphere Archive and Distribution System Distributed Active Archive Center. doi:10.5067/VIIRS/VNP46A4.002.

MitchellCo reports the source radiance in nW/(cm²·sr). It is an upward-emitted/nighttime radiance measure, not a Bortle class and not a direct measurement of zenith sky brightness.

NOAA / National Weather Service API

Forecast data

Cloud-cover values come from the NOAA/NWS API and retain their forecast time. NWS states that its web information is public domain unless specifically noted otherwise and requires users not to imply government endorsement or present modified content as official government material.

MitchellCo's viewing score is derived from source data and is not an official NOAA/NWS forecast. Internet delivery is not guaranteed.

OpenStreetMap

Basemap

Attribution: © OpenStreetMap contributors. OpenStreetMap data are available under the Open Data Commons Open Database License (ODbL). MitchellCo's web maps use the standard OSM tile service only for normal interactive viewing and do not intentionally bulk-download or prefetch tiles.

Leaflet 1.9.4

Map rendering software

Interactive map rendering uses Leaflet 1.9.4, distributed under the BSD-2-Clause license.

MitchellCo Tonight Score v2

For Map 26, only forecast-covered samples with Sun altitude at or below −18° count as astronomical darkness. The algorithm searches the next 24 hours for the best contiguous three-hour dark window. Its core score is 50% transformed annual VIIRS radiance, 35% NWS clear-sky percentage, and 15% Moon score. Moon interference uses illumination and altitude and becomes zero when the Moon is below the horizon. The final score is 90% of that best-window core plus 10% based on total forecast-covered astronomical-dark hours. This is a MitchellCo heuristic for comparative planning context, not an official astronomical forecast.

Map 27 · Your Compass Lies

NOAA NCEI / British Geological Survey · World Magnetic Model 2025

Global geomagnetic reference model

Map 27 uses the standard degree/order-12 WMM2025 coefficients locally in the browser. The coefficient file is stored same-origin at data/WMM2025.COF, and a normalized subset of NOAA's official validation vectors is stored at data/wmm2025-test-values.json. No magnetic-model service is called when a visitor clicks the map.

Dataset citation: NOAA NCEI Geomagnetic Modeling Team; British Geological Survey. 2024: World Magnetic Model 2025. NOAA National Centers for Environmental Information. doi:10.25921/aqfd-sd83. Accessed 2026-09-24.

Reuse: NOAA states that the WMM source code is public domain, that its information/software may be used freely by the public, and that NOAA-produced material is not subject to U.S. copyright protection. This page identifies the incorporated U.S. Government material as required for cautious redistribution. No government or BGS endorsement is implied.

Validation: the local coefficient file is pinned to SHA-256 06791cd95faba7bdf4a709808f2715a53fe689b29c23b9886bc2196fa9b3eb13. Before enabling calculations, Map 27 evaluates six NOAA surface test vectors spanning 2025.0 and 2027.5 and checks field components plus secular variation against the published rounded values.

Interpretation: WMM models the long-wavelength internal magnetic field. NOAA states that crustal, upper-mantle, ionospheric and magnetospheric effects are not fully represented; a physical compass can also be disturbed by local magnetic material. Declination is therefore a model value, not a local magnetic survey. Map 27 flags NOAA's caution zone at 2,000–6,000 nT horizontal intensity and blackout/unreliable zone below 2,000 nT.

Release philosophy

When a source requires a specific notice, year, copyright statement, citation, or license link, MitchellCo retains it. If the required year is not known from the source data, publication is held rather than guessed. Sources with unresolved commercial-use or redistribution terms are excluded until cleared.