Flood, wetland, shoreline, conservation, and natural-hazard information can change where or how a project is assessed and which approvals are needed. Begin with the official map or screening tool for the property, but do not treat a mapped result—or an empty result—as a site determination. The map identifies a question to resolve with the authority responsible for the proposed work.

Use a screening-to-decision sequence

  1. Match the property. Confirm the parcel boundary, address, and governing authority before interpreting a map. Note the map panel, layer, dataset, model, and date or imagery vintage shown.
  2. Identify the trigger. Find out whether the proposed work is in or near a mapped flood area, watercourse, wetland, shoreline, conservation area, critical area, or other regulated zone. Check local definitions of development and regulated activity; a small accessory dwelling may still trigger a review.
  3. Ask what determination is needed. Depending on the jurisdiction and site, the next step may be a parcel-specific agency determination, wetland delineation, flood or soil assessment, survey, conservation permit, or other technical review. Ask which authority accepts the work and what study or application it requires.
  4. Check the complete approval path. A zoning result does not replace environmental, conservation, building, septic, or floodplain approvals. Confirm any exemptions, conditions, notices, appeals, and permit sequence with each responsible office before relying on a project layout.

Know what common map products establish

In the United States, FEMA’s National Flood Hazard Layer and Flood Insurance Rate Maps are official National Flood Insurance Program flood-hazard products. Check the effective map for the community and parcel, including any applicable Letter of Map Revision. A flood-map result is not an elevation certificate, site-specific engineering analysis, or complete statement of state and local requirements.

Different screening products answer different questions. NOAA’s coastal flood-frequency layer is a planning screen for potential coastal flooding, not an exact site location or permitting product. USDA’s Web Soil Survey gives interactive access to current electronic soil information for available survey areas. Define an Area of Interest (AOI) before viewing soil data; it can be drawn as a rectangle or polygon, imported from a shapefile, or set to a whole Soil Survey Area. The Soil Map and Soil Data Explorer can provide map units, soil properties, ratings, and reports. Use the AOI and report to identify questions for follow-up: a mapped soil unit or rating does not establish foundation performance, drainage design, or engineering suitability. State environmental GIS layers can point to records worth checking; their presence or absence does not by itself establish a legal wetland boundary or a permit trigger.

In the United States, the Army Corps of Engineers’ National Levee Database can report estimated people, buildings, and property value behind a levee system. These are computer-generated, area-level comparisons with federal datasets whose source years differ; they are not parcel appraisals, flood probabilities, levee certifications, or guarantees that a levee will prevent flooding. Check whether the system has a more recent risk assessment or review, then ask the responsible floodplain or levee authority about current system condition and local flood records.

For a U.S. coastal site, use the Fish and Wildlife Service’s official Coastal Barrier Resources System (CBRS) map and its validation route when checking whether a location is in the system. Digital boundaries approximate the official maps and are not a basis for federal funding eligibility; obtain a formal determination when that status matters. For a FEMA flood-map question, compare the LOMA, LOMR-F, LOMR, and CLOMR routes; each addresses a different map or project condition.

For a Canadian flood map, record the study date, the process it models, and the authority responsible for the local product. Natural Resources Canada’s technical guidance explains that maps represent watershed, floodplain, and river conditions when the study was completed; major floods, wildfire, land-use changes, channel movement, erosion, or changes to flood infrastructure may affect whether an older study remains useful. These are reasons for a qualified practitioner or authority to review a map, not automatic legal expiry rules. Flood management is provincial and territorial, so confirm current map status and requirements with the responsible jurisdiction. A hazard map also does not measure all of the people or infrastructure vulnerability needed for a risk assessment.

British Columbia says floodplain maps are screening and planning information: flooding can occur outside mapped areas or exceed estimated levels, and return periods are probabilities in each year rather than a schedule. In Alberta, the provincial flood-hazard dataset has irregular updates and directs users to check GeoDiscover for the latest version; catalog coverage dates and modification dates do not confirm a parcel result. Wales uses a separate planning map under TAN 15; see how to distinguish it from the present-day defended-risk viewer.

The U.S. Fish and Wildlife Service’s National Wetlands Inventory maps wetlands and deepwater habitats for discovery and decision support. It uses a biological inventory approach; the mapper does not determine the jurisdiction or boundaries of every federal, state, Tribal, or local wetland program. A mapped feature can require agency review, and no mapped feature does not prove that a site is free of regulated wetlands. Record the release or imagery date shown for the feature because mapped areas can have different source dates.

Canada’s federal Critical Habitat for Species at Risk dataset is another screening layer, with a different purpose and coverage. The national dataset includes selected terrestrial species where Environment and Climate Change Canada or Parks Canada has responsibility; it may contain generalized or archived records and is not a legally authoritative parcel boundary. For the species-specific meaning and current critical-habitat description, check the recovery strategy or action plan in the Species at Risk Public Registry. See how to check Canada’s critical-habitat map for an ADU site. A missing or generalized map feature is not a parcel clearance.

In Ontario, development in a conservation authority’s regulated area can require a separate permit. The authority’s map and rules identify where to ask, but the parcel-specific determination and applicable activity requirements must be confirmed with that authority. Scotland’s SEPA address search screens a circular area with a 50-metre radius; use the interactive map to inspect the site itself and check available flood sources and likelihoods, including future scenarios. An empty map result does not clear a site: some small watercourses and ground features may not be modelled, and a site near an extent can still merit investigation. If a proposal is in or near mapped risk, SEPA recommends checking local flood history, protection schemes, detailed studies, and council information. A qualified professional may need to prepare a Flood Risk Assessment; that assessment does not guarantee the site is suitable.

In England, the Environment Agency directs planning applicants to use the Flood Map for Planning together with the local planning authority’s Strategic Flood Risk Assessment to research a development site. Its standing advice asks users to assess the production date, purpose, and limitations of the data. Separately, particular activities on or near a main river, floodplain, culvert, or defence can require an environmental permit even when a flood map is not the deciding test. Check England’s activity-based flood-risk permit triggers and confirm the exact work and distance with the Environment Agency. Whether an ADU needs a flood-risk assessment or permit depends on the current guidance, site, project type, and local circumstances; neither process can be decided for an unspecified property.

England’s groundwater source-protection zones are a separate environmental screen, especially when a proposal involves a septic-tank soakaway, another discharge to ground, or work with a potential pollution pathway. The Environment Agency’s zones are modelled around abstractions used for domestic supply or food production; a zone does not itself decide an ADU permit route. Check the England groundwater source-protection map and its limits, then ask the authority about the proposed activity.

England also has locally selected nature-conservation records that are distinct from national statutory designations. Check Local Wildlife and Local Geological Site records and the local plan; a local-site flag is not by itself a parcel-specific prohibition or approval decision.

State wetland programs add their own steps. Maine DEP warns that National Wetlands Inventory maps are general guidance and that unmapped or inaccurately drawn wetlands may need a site inspection. Michigan EGLE’s Wetland Identification Program was designed in part for relatively small, non-commercial projects such as a single house or outbuilding. Level 2 is an EGLE on-site review of a defined WIP Review Area of up to five acres; Level 3 verifies a wetland professional’s previously completed delineation and has no acreage limit. For either service, EGLE’s three-year guarantee applies only to regulated wetland areas inside the official WIP Review Area, and WIP is not a wetland permit. Discuss service suitability and the exact review boundary with EGLE before relying on a report.

In the United States, a site with a mining history may need records beyond a national map. USGS says its USMIN abandoned hardrock-mine inventory is still being assembled and that no comprehensive national inventory of abandoned mine features exists. A blank national search therefore cannot show that a parcel has no shaft, adit, subsidence, or mine-related environmental concern. Check relevant state, Tribal, local, and historical records where mining may have occurred, and get a site-specific assessment if the property record or observed conditions raise a concern. Hardrock-mine records and coal-mine records are separate searches.

Other regional checks answer different questions. In British Columbia, the Riparian Areas Protection Regulation uses a qualified environmental professional’s site assessment to establish the applicable streamside protection area; do not infer a universal setback from a stream map. In Alberta, old water-well records may be missing or plotted approximately, while abandoned wells are a separate development-permit check under current AER Directive 079. Confirm both record identity and the current local review route.

Radon maps also describe potential rather than a building’s measured indoor concentration. EPA’s U.S. county map is a resource-targeting screen and recommends testing homes in every zone. The Great Britain Radon Affected Areas dataset estimates area-level probability; a mapped category is not a test result. For ground movement, BGS GeoSure and the separate building-level Property Subsidence Assessment have different coverage and outputs; read their scale and model limits.

The U.S. national landslide product combines an event inventory with a 90-metre susceptibility model; inventory coverage varies and the model does not explicitly account for long runout. Use local, higher-resolution information where available and seek a geotechnical assessment when slopes or site history raise a concern. Canada’s Atlas permafrost map is a 2010 regional edition, not current parcel ground data. The Canadian seismic hazard tool supplies design inputs for NBC 2020 and 2025 based on coordinates and applicable site designation; confirm local code adoption and site inputs with the building authority and design professional.

California Fire Hazard Severity Zone maps classify modeled hazard rather than property-specific risk; confirm State or Local Responsibility Area status and local adoption. California’s separate regulatory seismic zones can trigger a site investigation before permitting; check the official EQ Zapp status and local process. For species screening, the U.S. Fish and Wildlife Service’s IPaC workflow and formal species-list process are distinct from a general habitat-map check; see the IPaC project-area review. Environmental-history searches also need program-specific sources and competent assessment; see the contaminated-site record routes. In former coal-mining areas of England, Scotland, and Wales, check the separate home-improvement map, assessment, and permit routes.

In England, surface-water planning extents also have stated scenario and dataset dates, but the dataset warns that area-level products are not suitable for deciding whether an individual property is at risk. Keep the map’s scenario and version with the result and obtain site-specific advice when the planning route requires it.

For U.S. wetland checks, keep identification and jurisdiction distinct. EPA describes the Clean Water Act Section 404 identification process in terms of soils, vegetation, and hydrology; an agency’s jurisdictional determination addresses whether identified waters are regulated under that program. New York’s state process offers a separate example: its parcel Jurisdictional Determination (JD) addresses whether regulated wetlands or adjacent areas are present within the requested boundary, but does not establish their extent. A positive parcel JD can be followed by wetland delineation and a Project JD; a negative state JD does not rule out a federal permit. New York DEC’s current page also reflects the April 8, 2026 court decision, states which previously mapped or larger wetlands can require an Article 24 application, and offers reassessment of some earlier JDs. See New York freshwater wetland checks for an ADU site for the current state process and date boundaries. State and federal routes differ, and one agency’s result does not automatically resolve every other program.

These examples are specific to their named jurisdictions. They do not supply a rule for a different state, province, nation, or municipality.

Keep the result useful without overstating it

For each check, keep the source, lookup date, parcel relationship, map/model version, and next confirming authority together. If an official layer is incomplete, has no visible date, or does not resolve the parcel, say so and request the underlying record. Do not convert a screening result into a claim that construction is safe, a permit is required or waived, or the ADU can be approved. Where a hazard or environmental condition could affect life safety or protected resources, wait for the responsible authority or qualified professional to provide the site-specific assessment before making design or siting decisions.