App Component

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Component Structure

export default function App(): JSX.Element

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State Management

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Map State

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Data State

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UI State

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Filter State

interface FilterState {
  jobTypes: Set<string>;    // Selected job types (NB, DM, GC, etc.)
  boroughs: Set<string>;    // Selected boroughs (MANHATTAN, BROOKLYN, etc.)
  daysBack: number;         // Date range in days (7 or 30)
}

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Key Functions

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buildTileSource

function buildTileSource(): TileSource

• width: 123,904 pixels
• height: 100,864 pixels
• tileSize: 512 pixels
• minLevel/maxLevel: Computed from DZI dimensions (8 zoom levels)
• getTileUrl: Function that maps OSD zoom level and tile coordinates to WebP tile URLs

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placeMarkers

const placeMarkers = useCallback(() => void, [filteredPermits, overlayOn])

• Nuclear clear: Removes all existing permit overlays by DOM class and ref tracking
• Recency fade: Pre-computes opacity values in O(n) based on permit date (older permits are more transparent)
• Chunked rendering: Adds markers in batches of 400 per frame using requestAnimationFrame to avoid blocking the main thread
• Event handlers: Attaches mouseenter, mouseleave, and click handlers to each marker
• Generation tracking: Uses markerGenRef to cancel stale RAF callbacks from previous renders

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placeHelicopters

const placeHelicopters = useCallback((helis: HelicopterState[]) => void, [])

• Smooth interpolation: Animates helicopter movement between position updates over 12 seconds
• Directional rotation: Flips helicopter emoji based on track (heading) angle
• Stale removal: Removes helicopter markers that are no longer in the active set
• RAF animation loop: Continuously updates positions using requestAnimationFrame

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flyToPermit

const flyToPermit = useCallback((permit: Permit) => void, [])

1. Parses latitude/longitude from the permit
2. Converts lat/lng to image pixel coordinates using latlngToImagePx()
3. Converts image coordinates to OpenSeadragon viewport coordinates
4. Pans to the target location
5. Zooms to level 6 (or maintains current zoom if already > 4)

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toggleJobType

const toggleJobType = (jt: string) => void

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toggleBorough

const toggleBorough = (b: string) => void

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computeOpacities

function computeOpacities(permits: Permit[]): Map<Permit, number>

1. Extracts timestamps from issued_date or approved_date
2. Finds min/max valid timestamps
3. Maps each permit to an opacity value from 0.5 to 1.0 (older = more transparent)
4. Returns a Map for O(1) lookup during marker rendering

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Sub-Components

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PermitChart

function PermitChart({ permits }: { permits: Permit[] }): JSX.Element | null

• Groups permits by job_type and counts occurrences
• Sorts by count (descending) and shows top 8 types
• Renders color-coded bars with glow effects
• Shows total permit count at the bottom

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PermitDrawer

function PermitDrawer({ 
  permit, 
  onClose 
}: { 
  permit: Permit; 
  onClose: () => void 
}): JSX.Element

• Color-coded header with job type emoji and label
• Address and location (neighborhood, borough, zip)
• Job description
• Filing details (type, status, dates)
• Estimated cost
• Owner, contractor, and expediter information
• BIN, BBL, and community board metadata
• External links to DOB BIS, ZoLa, Google Maps, and Street View

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PermitRow

function PermitRow({ 
  index, 
  style, 
  data 
}: ListChildComponentProps<PermitRowData>): JSX.Element

• Color-coded dot indicator matching job type
• Job type badge and issue date
• Formatted address
• Highlights when selected
• Click handler opens drawer and flies to location

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Effect Lifecycle

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OpenSeadragon Initialization

1. Creates OpenSeadragon viewer with custom tile source
2. Configures gesture settings (scroll to zoom, no click to zoom)
3. Sets up navigator (mini-map) for desktop only
4. Adds ‘open’ handler that:
   • Sets dziLoaded to true
   • Creates NeighborhoodLabels instance
   • Pans to Midtown Manhattan (Empire State Building)
   • Zooms to 3.5 (desktop) or 10 (mobile)
5. Cleanup function destroys viewer and labels on unmount

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Permit Data Fetching

1. Calls fetchPermits(filters.daysBack) API
2. Updates permits state on success
3. Sets error state on failure
4. Re-fetches every 5 minutes (300,000ms interval)
5. Cleanup function clears the interval

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Helicopter Live Layer

1. Waits for dziLoaded to be true
2. Calls fetchHelicopters() API
3. Passes results to placeHelicopters()
4. Repeats every 12 seconds
5. Cleanup function cancels polling

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Marker Rendering

1. Waits for dziLoaded to be true
2. Calls placeMarkers() when filteredPermits or overlayOn changes

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Virtual List Scrolling

1. Finds index of selectedPermit in sortedPermits
2. Calls listRef.current.scrollToItem(idx, 'smart')

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Marker Highlighting

1. Removes permit-marker--selected class from all markers
2. Finds the marker element by key (e.g., job-{filing_number})
3. Adds permit-marker--selected class to the matching marker

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Usage Example

import App from './App';
import './App.css';

function Root() {
  return <App />;
}

export default Root;

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Performance Optimizations

1. Chunked marker rendering: Adds markers in batches of 400 per frame to avoid blocking the main thread
2. Memoized filtering: Uses useMemo for filteredPermits and sortedPermits to avoid redundant computations
3. Pre-computed opacities: Calculates marker opacity values in O(n) instead of O(n²)
4. Virtual scrolling: Uses react-window to render only visible permit list rows
5. Dynamic list height: Uses ResizeObserver to measure list container height for accurate virtualization
6. RAF animation loops: Uses requestAnimationFrame for smooth helicopter and marker animations
7. Generation tracking: Cancels stale RAF callbacks when filters change

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Dependencies

• react - Core React library
• openseadragon - Deep zoom image viewer
• react-window - Virtual scrolling for permit list
• Custom utilities: latlngToImagePx, fetchPermits, fetchHelicopters, getJobColor, getJobEmoji, getJobLabel, formatAddress, formatDate
• NeighborhoodLabels - Custom overlay manager for neighborhood labels

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See Also

• NeighborhoodLabels - Overlay manager for LOD neighborhood labels
• Permit Map - MapLibre alternative map view