diff --git a/assets/js/rover_map_hook.ts b/assets/js/rover_map_hook.ts
index aca7abec..0b9f9b71 100644
--- a/assets/js/rover_map_hook.ts
+++ b/assets/js/rover_map_hook.ts
@@ -28,6 +28,7 @@ interface RoverMapHook extends ViewHook {
   qualityLayer: L.GridLayer | null
   selectedCandidateMarker: L.CircleMarker | null
   candidatePathLayer: L.LayerGroup
+  candidateBuildingsLayer: L.LayerGroup
   gridLayer: L.LayerGroup
   gridVisible: boolean
   cellLookup: Map<string, Cell>
@@ -90,6 +91,7 @@ export const RoverMap: Partial<RoverMapHook> = {
     this.qualityLayer = null
     this.selectedCandidateMarker = null
     this.candidatePathLayer = L.layerGroup()
+    this.candidateBuildingsLayer = L.layerGroup()
     this.gridLayer = L.layerGroup()
     this.gridVisible = true
     this.cellLookup = new Map()
@@ -183,6 +185,7 @@ export const RoverMap: Partial<RoverMapHook> = {
     map.fitBounds(this.driveCircle.getBounds(), { padding: [20, 20] })
 
     this.candidatePathLayer.addTo(map)
+    this.candidateBuildingsLayer.addTo(map)
     this.gridLayer.addTo(map)
     updateGridOverlay(map, this.gridLayer)
 
@@ -294,6 +297,30 @@ export const RoverMap: Partial<RoverMapHook> = {
         ).addTo(this.candidatePathLayer)
       }
     })
+
+    this.handleEvent("candidate_buildings", (
+      { buildings }: {
+        buildings: { lat: number; lon: number; radius_m: number; height_m: number }[]
+      }
+    ) => {
+      this.candidateBuildingsLayer.clearLayers()
+      if (!buildings || buildings.length === 0) return
+
+      for (const b of buildings) {
+        // Color by height: tall = red, medium = orange, low = yellow.
+        const color = b.height_m >= 30 ? "#dc2626" : b.height_m >= 10 ? "#f97316" : "#facc15"
+        L.circle([b.lat, b.lon], {
+          radius: Math.max(b.radius_m, 8),
+          color,
+          weight: 1,
+          fillColor: color,
+          fillOpacity: 0.45,
+          interactive: true
+        })
+          .bindTooltip(`${Math.round(b.height_m)} m`, { direction: "top", offset: [0, -4] })
+          .addTo(this.candidateBuildingsLayer)
+      }
+    })
   },
 
   reconnected(this: RoverMapHook) {
diff --git a/lib/microwaveprop/application.ex b/lib/microwaveprop/application.ex
index f09a4a96..596af17f 100644
--- a/lib/microwaveprop/application.ex
+++ b/lib/microwaveprop/application.ex
@@ -24,6 +24,7 @@ defmodule Microwaveprop.Application do
       {PartitionSupervisor,
        child_spec: Task.Supervisor, name: Microwaveprop.TaskSupervisor, partitions: System.schedulers_online()},
       Microwaveprop.Cache,
+      Microwaveprop.Buildings.Index,
       Microwaveprop.Propagation.ScoreCache,
       Microwaveprop.Weather.GridCache,
       {Microwaveprop.Weather.IemRateLimiter,
diff --git a/lib/microwaveprop/buildings/index.ex b/lib/microwaveprop/buildings/index.ex
new file mode 100644
index 00000000..c91de048
--- /dev/null
+++ b/lib/microwaveprop/buildings/index.ex
@@ -0,0 +1,164 @@
+defmodule Microwaveprop.Buildings.Index do
+  @moduledoc """
+  In-memory spatial index over Microsoft building footprint records.
+  Buckets buildings into a ~1.1 km grid so that a max-height query in
+  a small radius scans only the 9 nearest buckets.
+
+  Records (`Microwaveprop.Buildings.Parser.record`) are bucketed by
+  centroid; queries widen by the building's `max_radius_m` so a long
+  warehouse straddling two buckets is still found by points in either.
+
+  Loading is one-shot per tile (idempotent via the `:loaded_tiles`
+  bucket). Queries hit ETS directly with no GenServer involvement.
+  """
+
+  use GenServer
+
+  alias Microwaveprop.Buildings.Parser
+
+  @table :buildings_spatial_index
+  @loaded_tiles_table :buildings_loaded_tiles
+  # 0.01° ≈ 1.1 km at our latitude — strikes a balance between
+  # bucket scan size and number of empty buckets allocated.
+  @bucket_step 0.01
+
+  @spec start_link(keyword()) :: GenServer.on_start()
+  def start_link(opts), do: GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+
+  @impl true
+  def init(_opts) do
+    ensure_tables()
+    {:ok, %{}}
+  end
+
+  @doc """
+  Returns the list of building records within `radius_m` of `(lat, lon)`.
+  Same scan path as `max_height_near/3` — useful for surfacing the
+  individual obstacles to a UI layer.
+  """
+  @spec records_near(float(), float(), number()) :: [Parser.record()]
+  def records_near(lat, lon, radius_m) do
+    ensure_tables()
+    radius_deg = radius_m / 111_000.0
+    cos_lat = :math.cos(lat * :math.pi() / 180.0)
+
+    {min_bx, max_bx} =
+      bucket_range(lon - radius_deg / max(cos_lat, 0.1), lon + radius_deg / max(cos_lat, 0.1))
+
+    {min_by, max_by} = bucket_range(lat - radius_deg, lat + radius_deg)
+
+    for by <- min_by..max_by,
+        bx <- min_bx..max_bx,
+        {_, list} <- :ets.lookup(@table, {bx, by}),
+        rec <- list,
+        within?(rec, lat, lon, cos_lat, radius_m) do
+      rec
+    end
+  end
+
+  defp within?(rec, lat, lon, cos_lat, radius_m) do
+    dlat_m = (rec.centroid_lat - lat) * 111_000.0
+    dlon_m = (rec.centroid_lon - lon) * 111_000.0 * cos_lat
+    dist_m = :math.sqrt(dlat_m * dlat_m + dlon_m * dlon_m)
+    dist_m - rec.max_radius_m <= radius_m
+  end
+
+  @doc """
+  Returns the maximum building `height_m` within `radius_m` of
+  `(lat, lon)`. `0.0` if no buildings indexed within the radius.
+  """
+  @spec max_height_near(float(), float(), number()) :: float()
+  def max_height_near(lat, lon, radius_m) do
+    ensure_tables()
+    radius_deg = radius_m / 111_000.0
+    cos_lat = :math.cos(lat * :math.pi() / 180.0)
+
+    {min_bx, max_bx} = bucket_range(lon - radius_deg / max(cos_lat, 0.1), lon + radius_deg / max(cos_lat, 0.1))
+    {min_by, max_by} = bucket_range(lat - radius_deg, lat + radius_deg)
+
+    for by <- min_by..max_by,
+        bx <- min_bx..max_bx,
+        {_, list} <- :ets.lookup(@table, {bx, by}),
+        reduce: 0.0 do
+      acc -> max(acc, scan_bucket(list, lat, lon, cos_lat, radius_m))
+    end
+  end
+
+  defp scan_bucket(list, lat, lon, cos_lat, radius_m) do
+    Enum.reduce(list, 0.0, fn rec, acc ->
+      dlat_m = (rec.centroid_lat - lat) * 111_000.0
+      dlon_m = (rec.centroid_lon - lon) * 111_000.0 * cos_lat
+      dist_m = :math.sqrt(dlat_m * dlat_m + dlon_m * dlon_m)
+
+      if dist_m - rec.max_radius_m <= radius_m,
+        do: max(acc, rec.height_m),
+        else: acc
+    end)
+  end
+
+  @doc """
+  Insert a list of `Parser.record/0` maps into the spatial index.
+  Idempotent at the tile level (callers gate via `loaded?/1`); within
+  a tile, inserting the same record twice will produce a duplicate
+  entry but will not affect query correctness.
+  """
+  @spec insert_records([Parser.record()]) :: :ok
+  def insert_records(records) when is_list(records) do
+    ensure_tables()
+
+    records
+    |> Enum.group_by(fn r -> {bucket_x(r.centroid_lon), bucket_y(r.centroid_lat)} end)
+    |> Enum.each(fn {key, recs} ->
+      existing =
+        case :ets.lookup(@table, key) do
+          [{_, list}] -> list
+          [] -> []
+        end
+
+      :ets.insert(@table, {key, recs ++ existing})
+    end)
+
+    :ok
+  end
+
+  @doc "Mark a quadkey as loaded so callers can skip re-parsing its tile."
+  @spec mark_loaded(String.t()) :: :ok
+  def mark_loaded(quadkey) do
+    ensure_tables()
+    :ets.insert(@loaded_tiles_table, {quadkey, true})
+    :ok
+  end
+
+  @spec loaded?(String.t()) :: boolean()
+  def loaded?(quadkey) do
+    ensure_tables()
+    :ets.member(@loaded_tiles_table, quadkey)
+  end
+
+  @doc "Wipe all index state (test helper / dev convenience)."
+  @spec clear() :: :ok
+  def clear do
+    ensure_tables()
+    :ets.delete_all_objects(@table)
+    :ets.delete_all_objects(@loaded_tiles_table)
+    :ok
+  end
+
+  defp ensure_tables do
+    if :ets.whereis(@table) == :undefined do
+      :ets.new(@table, [:set, :named_table, :public, read_concurrency: true])
+    end
+
+    if :ets.whereis(@loaded_tiles_table) == :undefined do
+      :ets.new(@loaded_tiles_table, [:set, :named_table, :public, read_concurrency: true])
+    end
+  end
+
+  defp bucket_range(min, max) do
+    {bucket_index(min), bucket_index(max)}
+  end
+
+  defp bucket_x(lon), do: bucket_index(lon)
+  defp bucket_y(lat), do: bucket_index(lat)
+  defp bucket_index(v), do: trunc(Float.floor(v / @bucket_step))
+end
diff --git a/lib/microwaveprop/buildings/loader.ex b/lib/microwaveprop/buildings/loader.ex
new file mode 100644
index 00000000..bbe97bd3
--- /dev/null
+++ b/lib/microwaveprop/buildings/loader.ex
@@ -0,0 +1,60 @@
+defmodule Microwaveprop.Buildings.Loader do
+  @moduledoc """
+  Lazily loads cached Microsoft footprint csv.gz tiles into the
+  spatial `Microwaveprop.Buildings.Index`. Idempotent: a quadkey
+  loaded once stays loaded for the lifetime of the BEAM.
+
+  Tiles that haven't been pre-fetched are skipped with a debug log —
+  the rover scorer falls back to terrain-only path analysis when the
+  index is missing for a region.
+  """
+
+  alias Microwaveprop.Buildings.Index
+  alias Microwaveprop.Buildings.MsFootprints
+  alias Microwaveprop.Buildings.Parser
+
+  require Logger
+
+  @zoom 9
+
+  @doc """
+  Ensures every quadkey covering `bbox` has its csv.gz tile parsed
+  into the index. Returns the list of quadkeys that were *attempted*
+  (whether already loaded, freshly loaded, or missing on disk).
+  """
+  @spec ensure_loaded_for_bbox(map()) :: [String.t()]
+  def ensure_loaded_for_bbox(bbox) do
+    quadkeys = MsFootprints.quadkeys_for_bbox(bbox, @zoom)
+    Enum.each(quadkeys, &ensure_loaded/1)
+    quadkeys
+  end
+
+  @doc """
+  Load a single quadkey. No-op if already loaded; logs and skips if
+  the csv.gz file is missing on disk.
+  """
+  @spec ensure_loaded(String.t()) :: :ok
+  def ensure_loaded(quadkey) do
+    if Index.loaded?(quadkey) do
+      :ok
+    else
+      do_load(quadkey)
+    end
+  end
+
+  defp do_load(quadkey) do
+    path = Path.join(MsFootprints.cache_dir(), "#{quadkey}.csv.gz")
+
+    if File.exists?(path) do
+      records = path |> Parser.parse_tile() |> Enum.to_list()
+      Index.insert_records(records)
+      Index.mark_loaded(quadkey)
+      Logger.info("buildings index: loaded #{quadkey} (#{length(records)} polygons)")
+    else
+      Logger.debug("buildings index: tile #{quadkey} not on disk; skipping")
+      Index.mark_loaded(quadkey)
+    end
+
+    :ok
+  end
+end
diff --git a/lib/microwaveprop/buildings/parser.ex b/lib/microwaveprop/buildings/parser.ex
new file mode 100644
index 00000000..aff657bf
--- /dev/null
+++ b/lib/microwaveprop/buildings/parser.ex
@@ -0,0 +1,79 @@
+defmodule Microwaveprop.Buildings.Parser do
+  @moduledoc """
+  Streaming parser for Microsoft Building Footprint csv.gz tiles.
+
+  Each line is a GeoJSON `Feature` whose `geometry.coordinates` is a
+  Polygon (or MultiPolygon) and whose `properties.height` is meters
+  above ground. We collapse each polygon to a centroid + bounding
+  radius — that's all the rover path-clearance scorer needs, and it
+  keeps the in-memory footprint to ~32 bytes per building.
+
+  Polygons with `height = -1.0` (no estimate from the ML model) are
+  dropped — including them would just add noise.
+  """
+
+  @type record :: %{
+          centroid_lat: float(),
+          centroid_lon: float(),
+          max_radius_m: float(),
+          height_m: float()
+        }
+
+  @doc """
+  Returns a `Stream` of `t:record/0` for every polygon in `path` whose
+  height is known. Lazy; suitable for tiles with millions of rows.
+  """
+  @spec parse_tile(String.t()) :: Enumerable.t()
+  def parse_tile(path) do
+    path
+    |> File.stream!([:read, :compressed])
+    |> Stream.flat_map(&parse_line/1)
+  end
+
+  defp parse_line(line) do
+    case Jason.decode(String.trim(line)) do
+      {:ok, %{"properties" => %{"height" => h}, "geometry" => geom}} when h > 0.0 ->
+        case ring_from_geometry(geom) do
+          [] -> []
+          ring -> [build_record(ring, h)]
+        end
+
+      _ ->
+        []
+    end
+  end
+
+  defp ring_from_geometry(%{"type" => "Polygon", "coordinates" => [outer | _]}), do: outer
+  defp ring_from_geometry(%{"type" => "MultiPolygon", "coordinates" => [[outer | _] | _]}), do: outer
+  defp ring_from_geometry(_), do: []
+
+  defp build_record(ring, height) do
+    {sum_lat, sum_lon, n, min_lat, min_lon, max_lat, max_lon} =
+      Enum.reduce(ring, {0.0, 0.0, 0, 90.0, 180.0, -90.0, -180.0}, fn
+        [lon, lat], {sl, slon, n, mnla, mnlo, mxla, mxlo} ->
+          {
+            sl + lat,
+            slon + lon,
+            n + 1,
+            min(mnla, lat),
+            min(mnlo, lon),
+            max(mxla, lat),
+            max(mxlo, lon)
+          }
+      end)
+
+    centroid_lat = sum_lat / n
+    centroid_lon = sum_lon / n
+
+    # Approximate max radius: half-diagonal of the bbox in meters.
+    dlat_m = (max_lat - min_lat) * 111_000.0 / 2.0
+    dlon_m = (max_lon - min_lon) * 111_000.0 * :math.cos(centroid_lat * :math.pi() / 180.0) / 2.0
+
+    %{
+      centroid_lat: centroid_lat,
+      centroid_lon: centroid_lon,
+      max_radius_m: :math.sqrt(dlat_m * dlat_m + dlon_m * dlon_m),
+      height_m: height * 1.0
+    }
+  end
+end
diff --git a/lib/microwaveprop/rover/compute.ex b/lib/microwaveprop/rover/compute.ex
index 49e8eed8..055aee52 100644
--- a/lib/microwaveprop/rover/compute.ex
+++ b/lib/microwaveprop/rover/compute.ex
@@ -7,6 +7,7 @@ defmodule Microwaveprop.Rover.Compute do
   plus the top 5 candidate parking spots.
   """
 
+  alias Microwaveprop.Buildings.Loader, as: BuildingsLoader
   alias Microwaveprop.Propagation
   alias Microwaveprop.Radio.Maidenhead
   alias Microwaveprop.Rover.Aggregator
@@ -103,6 +104,7 @@ defmodule Microwaveprop.Rover.Compute do
 
     points = Enum.map(in_radius, &{&1.lat, &1.lon})
     elev_map = time_step("elev_lookup", fn -> elev_lookup.(points) end)
+    _ = time_step("buildings_load", fn -> BuildingsLoader.ensure_loaded_for_bbox(bbox) end)
     clearance_map = time_step("clearance", fn -> clearance_lookup.(in_radius, selected_stations) end)
     prominence_map = time_step("prominence", fn -> prominence_lookup.(in_radius) end)
 
diff --git a/lib/microwaveprop/rover/path_terrain.ex b/lib/microwaveprop/rover/path_terrain.ex
index 9410d07d..652d2c00 100644
--- a/lib/microwaveprop/rover/path_terrain.ex
+++ b/lib/microwaveprop/rover/path_terrain.ex
@@ -9,11 +9,18 @@ defmodule Microwaveprop.Rover.PathTerrain do
   clearance means the path is blocked by an intervening ridge.
   """
 
+  alias Microwaveprop.Buildings.Index, as: BuildingsIndex
   alias Microwaveprop.Rover.Elevation
 
   # Number of intermediate samples between rover and station.
   @sample_count 12
 
+  # Search radius around each path sample point when looking for
+  # buildings that obstruct the line of sight. ~150 m catches the
+  # typical width of a downtown high-rise plus a margin for building
+  # centroid imprecision.
+  @building_search_radius_m 150
+
   @type latlon :: {float(), float()}
 
   @doc """
@@ -25,6 +32,7 @@ defmodule Microwaveprop.Rover.PathTerrain do
   @spec clearance_map([map()], [map()], keyword()) :: %{{latlon(), latlon()} => integer() | nil}
   def clearance_map(cells, stations, opts \\ []) when is_list(cells) and is_list(stations) do
     elev_lookup = Keyword.get(opts, :elev_lookup, &Elevation.lookup_many/1)
+    buildings_lookup = Keyword.get(opts, :buildings_lookup, &default_building_height/1)
 
     pairs =
       for cell <- cells, station <- stations do
@@ -40,11 +48,11 @@ defmodule Microwaveprop.Rover.PathTerrain do
     elev = elev_lookup.(rover_points ++ sample_points)
 
     Map.new(pairs, fn {rover_pt, station_pt} ->
-      {{rover_pt, station_pt}, clearance(rover_pt, station_pt, elev)}
+      {{rover_pt, station_pt}, clearance(rover_pt, station_pt, elev, buildings_lookup)}
     end)
   end
 
-  defp clearance(rover_pt, station_pt, elev) do
+  defp clearance(rover_pt, station_pt, elev, buildings_lookup) do
     rover_elev = Map.get(elev, rover_pt)
 
     case rover_elev do
@@ -55,7 +63,7 @@ defmodule Microwaveprop.Rover.PathTerrain do
         path_max =
           rover_pt
           |> intermediate_samples(station_pt)
-          |> Enum.map(&Map.get(elev, &1))
+          |> Enum.map(&obstacle_top(&1, elev, buildings_lookup))
           |> Enum.reject(&is_nil/1)
           |> safe_max()
 
@@ -63,6 +71,20 @@ defmodule Microwaveprop.Rover.PathTerrain do
     end
   end
 
+  defp obstacle_top({lat, lon} = pt, elev, buildings_lookup) do
+    case Map.get(elev, pt) do
+      nil ->
+        nil
+
+      ground ->
+        ground + round(buildings_lookup.({lat, lon}))
+    end
+  end
+
+  defp default_building_height({lat, lon}) do
+    BuildingsIndex.max_height_near(lat, lon, @building_search_radius_m)
+  end
+
   defp intermediate_samples({lat1, lon1}, {lat2, lon2}) do
     # Linear interpolation in lat/lon — fine at the distances we work with
     # (≤200 mi). Skip endpoints (i=0 is the rover, i=N+1 is the station).
diff --git a/lib/microwaveprop_web/live/rover_live.ex b/lib/microwaveprop_web/live/rover_live.ex
index 1bcf9912..9f12fdce 100644
--- a/lib/microwaveprop_web/live/rover_live.ex
+++ b/lib/microwaveprop_web/live/rover_live.ex
@@ -9,6 +9,7 @@ defmodule MicrowavepropWeb.RoverLive do
   use MicrowavepropWeb, :live_view
 
   alias Microwaveprop.Accounts.User
+  alias Microwaveprop.Buildings.Index, as: BuildingsIndex
   alias Microwaveprop.Geocoder
   alias Microwaveprop.Propagation
   alias Microwaveprop.Radio.CallsignClient
@@ -287,6 +288,7 @@ defmodule MicrowavepropWeb.RoverLive do
 
       candidate ->
         detail = build_candidate_detail(candidate, socket)
+        paths = candidate_path_payload(detail, socket.assigns.fixed_stations)
 
         {:noreply,
          socket
@@ -294,7 +296,10 @@ defmodule MicrowavepropWeb.RoverLive do
          |> push_event("focus_cell", %{lat: candidate.lat, lon: candidate.lon, zoom: 11})
          |> push_event("candidate_paths", %{
            candidate: %{lat: candidate.lat, lon: candidate.lon},
-           paths: candidate_path_payload(detail, socket.assigns.fixed_stations)
+           paths: paths
+         })
+         |> push_event("candidate_buildings", %{
+           buildings: buildings_along_paths(candidate, paths)
          })}
     end
   end
@@ -303,7 +308,8 @@ defmodule MicrowavepropWeb.RoverLive do
     {:noreply,
      socket
      |> assign(selected_candidate: nil)
-     |> push_event("candidate_paths", %{candidate: nil, paths: []})}
+     |> push_event("candidate_paths", %{candidate: nil, paths: []})
+     |> push_event("candidate_buildings", %{buildings: []})}
   end
 
   def handle_event("rover_cell_detail", %{"lat" => lat, "lon" => lon}, socket) do
@@ -733,6 +739,34 @@ defmodule MicrowavepropWeb.RoverLive do
     Map.put(link, :profile_svg, profile_to_svg(link.profile))
   end
 
+  defp buildings_along_paths(candidate, paths) do
+    paths
+    |> Enum.flat_map(fn p ->
+      sample_along({candidate.lat, candidate.lon}, {p.station_lat, p.station_lon})
+    end)
+    |> Enum.flat_map(fn {lat, lon} ->
+      BuildingsIndex.records_near(lat, lon, 150)
+    end)
+    |> Enum.uniq_by(fn r -> {r.centroid_lat, r.centroid_lon} end)
+    |> Enum.map(fn r ->
+      %{
+        lat: r.centroid_lat,
+        lon: r.centroid_lon,
+        radius_m: r.max_radius_m,
+        height_m: r.height_m
+      }
+    end)
+  end
+
+  defp sample_along({lat1, lon1}, {lat2, lon2}) do
+    n = 24
+
+    for i <- 1..n do
+      f = i / (n + 1)
+      {lat1 + f * (lat2 - lat1), lon1 + f * (lon2 - lon1)}
+    end
+  end
+
   defp candidate_path_payload(detail, fixed_stations) do
     by_callsign = Map.new(fixed_stations, fn s -> {s.callsign, s} end)
 
diff --git a/test/microwaveprop/buildings/index_test.exs b/test/microwaveprop/buildings/index_test.exs
new file mode 100644
index 00000000..19767448
--- /dev/null
+++ b/test/microwaveprop/buildings/index_test.exs
@@ -0,0 +1,33 @@
+defmodule Microwaveprop.Buildings.IndexTest do
+  use ExUnit.Case, async: false
+
+  alias Microwaveprop.Buildings.Index
+
+  setup do
+    Index.clear()
+    :ok
+  end
+
+  test "max_height_near/3 returns 0 when no buildings have been indexed" do
+    assert Index.max_height_near(32.8, -97.0, 100) == 0.0
+  end
+
+  test "insert_records/1 then max_height_near/3 returns the tallest nearby height" do
+    Index.insert_records([
+      %{centroid_lat: 32.8000, centroid_lon: -97.0000, max_radius_m: 10.0, height_m: 8.0},
+      %{centroid_lat: 32.8001, centroid_lon: -97.0001, max_radius_m: 10.0, height_m: 25.0},
+      # Far away — should not be considered.
+      %{centroid_lat: 33.0, centroid_lon: -97.5, max_radius_m: 10.0, height_m: 100.0}
+    ])
+
+    assert Index.max_height_near(32.8000, -97.0000, 50) == 25.0
+  end
+
+  test "max_height_near/3 returns 0 when buildings are outside the radius" do
+    Index.insert_records([
+      %{centroid_lat: 32.8500, centroid_lon: -97.0500, max_radius_m: 10.0, height_m: 50.0}
+    ])
+
+    assert Index.max_height_near(32.8000, -97.0000, 100) == 0.0
+  end
+end
diff --git a/test/microwaveprop/buildings/parser_test.exs b/test/microwaveprop/buildings/parser_test.exs
new file mode 100644
index 00000000..d2b17c81
--- /dev/null
+++ b/test/microwaveprop/buildings/parser_test.exs
@@ -0,0 +1,40 @@
+defmodule Microwaveprop.Buildings.ParserTest do
+  use ExUnit.Case, async: true
+
+  alias Microwaveprop.Buildings.Parser
+
+  @sample_geojsonl """
+  {"type": "Feature", "properties": {"height": 5.5, "confidence": -1.0}, "geometry": {"type": "Polygon", "coordinates": [[[-97.736, 32.221], [-97.736, 32.222], [-97.735, 32.222], [-97.735, 32.221], [-97.736, 32.221]]]}}
+  {"type": "Feature", "properties": {"height": 12.0, "confidence": 0.9}, "geometry": {"type": "Polygon", "coordinates": [[[-97.0, 32.5], [-97.0, 32.501], [-96.999, 32.501], [-96.999, 32.5], [-97.0, 32.5]]]}}
+  {"type": "Feature", "properties": {"height": -1.0, "confidence": -1.0}, "geometry": {"type": "Polygon", "coordinates": [[[-97.5, 32.0], [-97.5, 32.001], [-97.499, 32.001], [-97.499, 32.0], [-97.5, 32.0]]]}}
+  """
+
+  setup do
+    path = Path.join(System.tmp_dir!(), "buildings_parser_#{:erlang.unique_integer([:positive])}.csv.gz")
+    gz = :zlib.gzip(@sample_geojsonl)
+    File.write!(path, gz)
+    on_exit(fn -> File.rm(path) end)
+    {:ok, path: path}
+  end
+
+  test "parse_tile/1 returns one record per polygon with height >= 0", %{path: path} do
+    records = path |> Parser.parse_tile() |> Enum.to_list()
+
+    assert length(records) == 2
+    assert Enum.all?(records, fn r -> r.height_m > 0 end)
+  end
+
+  test "parse_tile/1 returns centroid and max_radius_m per polygon", %{path: path} do
+    [first, _] = path |> Parser.parse_tile() |> Enum.to_list()
+
+    assert_in_delta first.centroid_lat, 32.2215, 0.001
+    assert_in_delta first.centroid_lon, -97.7355, 0.001
+    assert first.max_radius_m > 0
+    assert first.height_m == 5.5
+  end
+
+  test "parse_tile/1 skips polygons with height = -1", %{path: path} do
+    heights = path |> Parser.parse_tile() |> Enum.map(& &1.height_m)
+    refute -1.0 in heights
+  end
+end