Drive-Time & Trade Area Glossary

Block Group

Census Geography

A Census Bureau geographic unit containing approximately 600–3,000 people, nested within Census tracts and above individual blocks. Block groups are the smallest unit for which the American Community Survey (ACS) publishes full demographic profiles, including income, age, household size, housing tenure, and commute patterns. They are the standard aggregation unit for retail trade area demographic analysis because they offer a balance between geographic resolution and statistical reliability. Block group boundaries are updated at each decennial Census and do not always align with street networks, requiring interpolation when used with isochrone polygons.

Cannibalization

Network Planning

The reduction in sales at an existing location caused by opening a new company-owned location whose trade area overlaps with it. Cannibalization risk is proportional to the degree of primary trade area overlap: stores sharing more than 20–30% of their primary zones will typically show measurable same-store sales decline at the existing unit. Franchise systems manage cannibalization through protected territory clauses that prohibit new openings within a defined polygon around each franchisee's location. Accurate isochrone-based territories are more effective than radius-based protections because they reflect actual competitive reach.

Catchment Area

Trade Area Analysis

The population pool enclosed within a service or trade area boundary. Catchment analysis quantifies how many people live inside a given isochrone and characterizes their demographics — household income, age distribution, daytime vs. resident population. Healthcare planners, school districts, and library systems use "catchment area" most frequently; retailers and franchise developers often prefer "trade area," though the concepts are equivalent. The key metric derived from catchment analysis is population-per-unit, which drives revenue potential estimates.

Drive-Time Polygon

Isochrone Mapping

Retail industry synonym for isochrone. The term emphasizes that the boundary is defined by driving time rather than straight-line distance. Most site-selection software and franchise development teams use "drive-time polygon" and "isochrone" interchangeably, though "drive-time polygon" is more common in North American retail real estate contexts, while "isochrone" is preferred in European planning and academic literature.

Gravity Model

Demand Modeling

A probability-based framework for allocating customers across multiple competing locations as a function of store attractiveness and travel impedance. Borrowed from physics, gravity models assume that a store's drawing power increases with its size or attractiveness and decreases with distance or travel time. In practice, gravity models answer the question "given a customer at location X, which of our stores — or competitors' stores — will they choose?" They produce market share estimates for each store in a network and are used for site selection, cannibalization assessment, and network optimization.

Hub-and-Spoke

Logistics

A logistics network topology in which a central hub (distribution center, depot, or sorting facility) connects to multiple satellite stops or local delivery points. The hub aggregates volume, enabling economies of scale in long-haul transport, while the spokes handle local distribution. Drive-time isochrones from each hub define its serviceable territory and inform decisions about hub placement, the number of hubs required to cover a market, and which spokes fall within each hub's cost-efficient coverage zone. Hub-and-spoke networks are used in parcel delivery, food distribution, franchise supply chains, and public transit.

Huff Model

Demand Modeling

A specific gravity model formulated by David Huff in 1963 that estimates the probability of a consumer at a given location patronizing a particular retail facility. The Huff model defines attraction as a power function of store size (typically floor area) divided by a power function of travel time or distance. The probability of choosing store j equals store j's attraction divided by the sum of attractions from all stores in the competitive set. The model requires calibration of two parameters — the size exponent and the distance decay exponent — which vary by retail category and market type.

Isochrone

Isochrone Mapping

A polygon boundary enclosing all points reachable from an origin within a given travel time. Isochrones are computed via graph traversal on a road network rather than geometric expansion, so the shape reflects real-world road structure: expanding along highways, contracting at dead ends, and shifting around barriers like rivers or rail yards. The plural form "isochrones" is commonly used when multiple time bands are layered (e.g., 5, 10, and 15-minute rings). In retail analysis, isochrones replace radius buffers wherever accurate customer reach matters.

Last-Mile Delivery

Logistics

The final leg of a supply chain, from a distribution hub or fulfillment center to the end customer's address, typically covering the last 1–60 minutes of drive time. Last-mile delivery is the most expensive and operationally complex segment of logistics because it involves high-frequency, low-volume stops across variable urban and suburban road networks. Isochrones from a depot define the realistic coverage area within a target delivery time window, and they shift substantially by time of day due to traffic. Optimizing last-mile routes and depot locations requires accurate drive-time modeling rather than radius-based service area assumptions.

Median Household Income

Demographics

The income level at which half of households in a geographic area earn more and half earn less, published at the block group, tract, county, and national levels by the Census Bureau's American Community Survey. Median household income (MHI) is the primary demographic qualifier for most retail site selection models because it correlates with discretionary spending capacity. Analysts use MHI within a drive-time polygon to compare candidate sites against a brand's existing store base. MHI is a more robust indicator than mean income for retail purposes because it is less skewed by high earners at the top of the distribution.

OpenStreetMap (OSM)

Road Data

A collaborative open-source road network dataset maintained by volunteers globally and published under the Open Database License. OSM is the primary road data source for open-source routing engines including OSRM, Valhalla, and GraphHopper. Coverage quality varies by region: OSM is highly accurate in dense urban areas of North America and Western Europe but may have gaps or outdated speed data in rural or rapidly developing areas. Compared to commercial alternatives (HERE, TomTom), OSM is free to use but requires more engineering to operationalize for production isochrone generation.

Population Within Polygon

Demographics

The count of residents living inside a defined geographic boundary, typically an isochrone or trade area polygon. Population is aggregated from Census block groups or tracts using areal interpolation: Census unit populations are prorated by the fraction of the unit's area that falls within the polygon. Block group-level aggregation (roughly 600–3,000 people per unit) is the standard precision for retail trade area analysis. Daytime population — people present during working hours — can differ significantly from resident population and is relevant for lunch-focused food service and urban office corridor concepts.

Primary Trade Area

Trade Area Analysis

The innermost trade area band, typically the 5–10 minute drive zone that generates 60–70% of a store's customer transactions. Customers in the primary trade area shop the most frequently and are least likely to defect to a competitor. For most quick-service restaurants, grocery stores, and convenience concepts, the primary trade area is the single most important factor in revenue forecasting. Cannibalization risk from a nearby company store is highest when two primary trade areas significantly overlap.

Protected Territory

Franchise Development

A contractually defined geographic exclusivity zone granted to a franchisee, within which the franchisor agrees not to open a competing unit. Historically defined as a radius (e.g., "3-mile exclusive"), protected territories are increasingly defined as drive-time polygons to more accurately reflect competitive reach. A 3-mile radius in a dense urban grid is far smaller in effective customer reach than a 3-mile radius in a suburban arterial corridor — drive-time-based territories eliminate this inequity. Disputes over protected territory boundaries are among the most common sources of franchisor-franchisee litigation.

Radius Buffer

Isochrone Mapping

A fixed-distance circle drawn around a point location using straight-line (Euclidean) distance. Radius buffers are computationally trivial and easy to explain but systematically misrepresent actual market reach: they overstate coverage in areas with few roads and understate it along arterials and highways. A 5-mile radius in a grid-street urban core may correspond to a 7-minute drive on major roads, while the same circle in a rural area with limited crossings may represent a 20-minute drive. Radius buffers remain common in preliminary screening but should be replaced with isochrones for final site decisions.

Road Network Routing

Isochrone Mapping

The graph traversal algorithm used to compute travel times and isochrones across a road network. The road network is modeled as a directed weighted graph where nodes are intersections and edge weights represent travel time (distance ÷ speed limit, plus turn penalties). Dijkstra's algorithm or its variants (A*, bidirectional Dijkstra, contraction hierarchies) expand from the origin until all reachable nodes within the time budget are identified. The isochrone boundary is then interpolated between reachable and unreachable nodes. Accuracy depends on road data quality, speed profiles, and whether turn restrictions are encoded.

Secondary Trade Area

Trade Area Analysis

The ring surrounding the primary trade area, typically encompassing the 10–20 minute drive zone and accounting for 20–25% of customer transactions. Secondary trade area customers shop less frequently and are more price- and convenience-sensitive than primary customers. Competitive positioning matters more in the secondary zone: a superior competitor in the secondary area will erode share more significantly than one positioned only in the tertiary zone. Demographic analysis of the secondary trade area is critical for full-service restaurants and specialty retail.

Service Area

Logistics

The operational territory from which a business accepts orders or to which it dispatches vehicles or personnel. In logistics and delivery contexts, service areas are defined by maximum drive time from a depot or hub rather than by customer density. For emergency services, regulatory compliance may require a specific percentage of addresses to be reachable within a fixed time threshold. Service areas differ from trade areas in that they describe supply-side reach rather than demand-side attraction.

Site Selection

Retail Real Estate

The process of evaluating and ranking candidate retail or commercial locations against a defined set of criteria before committing to a lease or purchase. A structured site selection process typically includes trade area delineation, demographic scoring, competitive audit, traffic count analysis, co-tenancy evaluation, and financial modeling. Drive-time isochrones are used at the trade area delineation stage to define the realistic catchment from which customers can be expected to originate. Sophisticated retailers use predictive models trained on historical store performance to score new sites before any physical visits.

Tertiary Trade Area

Trade Area Analysis

The outermost band of a store's trade area, typically 30–60 minutes from the location and representing fringe or destination customers. The tertiary trade area contributes a small fraction of total transactions — often under 10% — but may be significant for destination concepts, anchor tenants, or businesses with no nearby competitors. Tertiary customers are the first to defect when a closer competitor opens. Some analysts omit the tertiary zone entirely from revenue models because its contribution falls within the margin of forecasting error.

Time-of-Day Traffic

Isochrone Mapping

The variation in road segment speeds across different hours of the day, which materially affects isochrone shape and size. A 15-minute isochrone generated at 2:00 AM from a suburban depot may extend 40% farther than the same isochrone generated at 8:00 AM peak commute. Routing engines that incorporate time-of-day profiles use historical speed data (typically from GPS probe records) to adjust edge weights by hour and day of week. For last-mile delivery planning and emergency service coverage, time-of-day isochrones are essential; for retail trade area analysis, an average or peak-period isochrone is usually sufficient.

Trade Area

Trade Area Analysis

The geographic zone from which a retail location draws the majority of its customers. Trade areas are typically divided into primary, secondary, and tertiary bands by customer frequency and drive time. Unlike administrative boundaries, trade areas are demand-derived: they reflect where customers actually live relative to the store, not where the nearest city limit falls. Analysts define them using customer address data, isochrones, gravity models, or a combination of all three.

Voronoi Diagram

Spatial Analysis

A spatial partition that assigns every point in a plane to the nearest of a set of seed locations, creating a tessellation of polygons with no gaps or overlaps. In retail analysis, Voronoi diagrams are sometimes used as a proxy for store trade areas by assigning each residential location to its nearest store. While computationally simple, Voronoi trade areas assume Euclidean distance and treat all stores as equally attractive regardless of size, format, or brand — limitations that make them significantly less accurate than gravity models or isochrone-based approaches. They remain useful for quick visual network gap analysis.