diff --git a/cmd/api_server.go b/cmd/api_server.go
index ccdef72..4ef8e67 100644
--- a/cmd/api_server.go
+++ b/cmd/api_server.go
@@ -27,11 +27,11 @@ func ApiServer(zipFile string, port int, debug bool) {
 	}
 
 	log.Printf("Loading CodePoint data from: %s", zipFile)
-	spatialIndex, err := spatialindex.NewCodePointSpatialIndex(zipFile)
+	idx, err := spatialindex.NewCodePointSpatialIndex(zipFile)
 	if err != nil {
 		log.Fatalf("failed to create spatial index: %v", err)
 	}
-	log.Printf("CodePoint spatial index created with %d entries", spatialIndex.Len())
+	log.Printf("CodePoint spatial index created with %d entries", idx.Len())
 
 	r := gin.New()
 
@@ -62,8 +62,8 @@ func ApiServer(zipFile string, port int, debug bool) {
 
 	cache := memoize.NewMemoizer(5*time.Minute, 10*time.Minute)
 
-	r.GET("/v1/postcode/codepoints", routes.CodePointSearch(spatialIndex))
-	r.GET("/v1/postcode/polygons", routes.PolygonSearch(spatialIndex, cache))
+	r.GET("/v1/postcode/codepoints", routes.CodePointSearch(idx))
+	r.GET("/v1/postcode/polygons", routes.PolygonSearch(idx, cache))
 
 	addr := fmt.Sprintf(":%d", port)
 	log.Printf("Starting HTTP API Server on port %d...", port)
diff --git a/routes/search.go b/routes/search.go
index 9fabd45..ef01027 100644
--- a/routes/search.go
+++ b/routes/search.go
@@ -26,7 +26,7 @@ type SearchResponse struct {
 
 const MAX_BOUNDS = 5000 // Maximum bounds in meters (5 KM)
 
-func CodePointSearch(spatialIndex *spatialindex.SpatialIndex) func(c *gin.Context) {
+func CodePointSearch(idx spatialindex.SpatialIndex) func(c *gin.Context) {
 	return func(c *gin.Context) {
 		bbox, err := parseBBox(c.Query("bbox"))
 		if err != nil {
@@ -39,7 +39,7 @@ func CodePointSearch(spatialIndex *spatialindex.SpatialIndex) func(c *gin.Contex
 			return
 		}
 
-		results, err := spatialIndex.Search(bbox)
+		results, err := idx.Search(bbox)
 		if err != nil {
 			log.Printf("error while fetching postcode data: %v", err)
 			c.JSON(http.StatusInternalServerError, gin.H{"error": "An internal server error occurred"})
@@ -53,7 +53,7 @@ func CodePointSearch(spatialIndex *spatialindex.SpatialIndex) func(c *gin.Contex
 	}
 }
 
-func PolygonSearch(spatialIndex *spatialindex.SpatialIndex, cache *memoize.Memoizer) func(c *gin.Context) {
+func PolygonSearch(idx spatialindex.SpatialIndex, cache *memoize.Memoizer) func(c *gin.Context) {
 	return func(c *gin.Context) {
 		bbox, err := parseBBox(c.Query("bbox"))
 		if err != nil {
@@ -71,7 +71,7 @@ func PolygonSearch(spatialIndex *spatialindex.SpatialIndex, cache *memoize.Memoi
 		requested := make(map[string]struct{}, 100)
 		districts := make(map[string]struct{}, 20)
 
-		err = spatialIndex.SearchIter(bbox, func(min, max [2]uint32, postcode string) bool {
+		err = idx.SearchIter(bbox, func(min, max [2]uint32, postcode string) bool {
 			district := strings.Split(postcode, " ")[0] // Take the first part of the postcode
 			districts[district] = struct{}{}
 			if tooBig {
diff --git a/spatial-index/codepoint.go b/spatial-index/codepoint.go
index d66ee50..b793fd0 100644
--- a/spatial-index/codepoint.go
+++ b/spatial-index/codepoint.go
@@ -16,12 +16,18 @@ type CodePoint struct {
 	Northing uint32 `json:"northing"`
 }
 
-type SpatialIndex struct {
+type SpatialIndex interface {
+	Search(bounds []uint32) (*[]CodePoint, error)
+	SearchIter(bounds []uint32, iter func(min, max [2]uint32, data string) bool) error
+	Len() int
+}
+
+type RtreeSpatialIndex struct {
 	tree *rtree.RTreeGN[uint32, string]
 }
 
-func NewCodePointSpatialIndex(zipFile string) (*SpatialIndex, error) {
-	idx := SpatialIndex{
+func NewCodePointSpatialIndex(zipFile string) (SpatialIndex, error) {
+	idx := RtreeSpatialIndex{
 		tree: &rtree.RTreeGN[uint32, string]{},
 	}
 
@@ -33,7 +39,7 @@ func NewCodePointSpatialIndex(zipFile string) (*SpatialIndex, error) {
 	return &idx, nil
 }
 
-func (idx *SpatialIndex) Search(bounds []uint32) (*[]CodePoint, error) {
+func (idx *RtreeSpatialIndex) Search(bounds []uint32) (*[]CodePoint, error) {
 
 	results := make([]CodePoint, 0, 100)
 	err := idx.SearchIter(bounds, func(min, max [2]uint32, data string) bool {
@@ -52,7 +58,7 @@ func (idx *SpatialIndex) Search(bounds []uint32) (*[]CodePoint, error) {
 	return &results, nil
 }
 
-func (idx *SpatialIndex) SearchIter(bounds []uint32, iter func(min, max [2]uint32, data string) bool) error {
+func (idx *RtreeSpatialIndex) SearchIter(bounds []uint32, iter func(min, max [2]uint32, data string) bool) error {
 	if len(bounds) != 4 {
 		return fmt.Errorf("search bounds must contain exactly 4 values: min_easting, min_northing, max_easting, max_northing")
 	}
@@ -64,11 +70,11 @@ func (idx *SpatialIndex) SearchIter(bounds []uint32, iter func(min, max [2]uint3
 	return nil
 }
 
-func (idx *SpatialIndex) Len() int {
+func (idx *RtreeSpatialIndex) Len() int {
 	return idx.tree.Len()
 }
 
-func (idx *SpatialIndex) importCodePoint(zipPath string) error {
+func (idx *RtreeSpatialIndex) importCodePoint(zipPath string) error {
 
 	r, err := zip.OpenReader(zipPath)
 	if err != nil {
@@ -92,7 +98,7 @@ func (idx *SpatialIndex) importCodePoint(zipPath string) error {
 	return nil
 }
 
-func (idx *SpatialIndex) processCSV(f *zip.File) error {
+func (idx *RtreeSpatialIndex) processCSV(f *zip.File) error {
 	r, err := f.Open()
 	if err != nil {
 		return fmt.Errorf("failed to open embedded file %s in zip: %w", f.Name, err)
diff --git a/spatial-index/codepoint_test.go b/spatial-index/codepoint_test.go
index 3806651..6cb5f1a 100644
--- a/spatial-index/codepoint_test.go
+++ b/spatial-index/codepoint_test.go
@@ -66,7 +66,7 @@ func TestSearch(t *testing.T) {
 }
 
 func TestSearchIter_InvalidBounds(t *testing.T) {
-	idx := &SpatialIndex{tree: &rtree.RTreeGN[uint32, string]{}}
+	idx := &RtreeSpatialIndex{tree: &rtree.RTreeGN[uint32, string]{}}
 	err := idx.SearchIter([]uint32{1, 2, 3}, func([2]uint32, [2]uint32, string) bool { return true })
 	require.Error(t, err)
 	require.Contains(t, err.Error(), "bounds must contain exactly 4 values")