From 9e199db27324e3b7cc7f2bcf151d7b8a9c9e00b9 Mon Sep 17 00:00:00 2001
From: Richard Hull <rm_hull@yahoo.co.uk>
Date: Sat, 28 Jun 2025 14:49:38 +0100
Subject: [PATCH 1/2] Inflate the bound box to include polygons whos centroids
 might be just outside the current bounds

---
 routes/search.go | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/routes/search.go b/routes/search.go
index ae8f4cd..f8cd04b 100644
--- a/routes/search.go
+++ b/routes/search.go
@@ -62,6 +62,10 @@ func PolygonSearch(spatialIndex *spatialindex.SpatialIndex, cache *memoize.Memoi
 		tooBig := isTooBig(bbox)
 		target := map[bool]string{true: "districts", false: "units"}[tooBig]
 
+		if target == "units" {
+			expandBounds(&bbox, 100)
+		}
+
 		requested := make(map[string]struct{}, 100)
 		districts := make(map[string]struct{}, 20)
 
@@ -110,6 +114,14 @@ func PolygonSearch(spatialIndex *spatialindex.SpatialIndex, cache *memoize.Memoi
 	}
 }
 
+func expandBounds(bbox *[]uint32, extendBy int) {
+	b := *bbox
+	b[0] = uint32(int(b[0]) - extendBy) // min_easting
+	b[1] = uint32(int(b[1]) - extendBy) // min_northing
+	b[2] = uint32(int(b[2]) + extendBy) // max_easting
+	b[3] = uint32(int(b[3]) + extendBy) // max_northing
+}
+
 func parseBBox(bboxStr string) ([]uint32, error) {
 	bboxParts := strings.Split(bboxStr, ",")
 	if len(bboxParts) != 4 {

From f940d46f4e7d272d2b5def7112dadcf69340643f Mon Sep 17 00:00:00 2001
From: Richard Hull <rm_hull@yahoo.co.uk>
Date: Sat, 28 Jun 2025 15:06:28 +0100
Subject: [PATCH 2/2] Address PR comments

---
 routes/search.go | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/routes/search.go b/routes/search.go
index f8cd04b..9fabd45 100644
--- a/routes/search.go
+++ b/routes/search.go
@@ -17,6 +17,8 @@ import (
 	"github.com/paulmach/orb/geojson"
 )
 
+const UNITS_BOUNDS_EXPANSION = 100
+
 type SearchResponse struct {
 	Results     []spatialindex.CodePoint `json:"results"`
 	Attribution []string                 `json:"attribution"`
@@ -63,7 +65,7 @@ func PolygonSearch(spatialIndex *spatialindex.SpatialIndex, cache *memoize.Memoi
 		target := map[bool]string{true: "districts", false: "units"}[tooBig]
 
 		if target == "units" {
-			expandBounds(&bbox, 100)
+			expandBounds(&bbox, UNITS_BOUNDS_EXPANSION)
 		}
 
 		requested := make(map[string]struct{}, 100)
@@ -114,12 +116,12 @@ func PolygonSearch(spatialIndex *spatialindex.SpatialIndex, cache *memoize.Memoi
 	}
 }
 
-func expandBounds(bbox *[]uint32, extendBy int) {
+func expandBounds(bbox *[]uint32, extendBy uint32) {
 	b := *bbox
-	b[0] = uint32(int(b[0]) - extendBy) // min_easting
-	b[1] = uint32(int(b[1]) - extendBy) // min_northing
-	b[2] = uint32(int(b[2]) + extendBy) // max_easting
-	b[3] = uint32(int(b[3]) + extendBy) // max_northing
+	b[0] -= extendBy // min_easting
+	b[1] -= extendBy // min_northing
+	b[2] += extendBy // max_easting
+	b[3] += extendBy // max_northing
 }
 
 func parseBBox(bboxStr string) ([]uint32, error) {