Tests of the three current strategies for reducing tile size

README.md

@@ -91,6 +91,7 @@ Options
  * -m _detail_ or --minimum-detail=_detail_: Minimum detail that it will try if tiles are too big at regular detail (default 7)
  * -b _pixels_ or --buffer=_pixels_: Buffer size where features are duplicated from adjacent tiles. Units are "screen pixels"--1/256th of the tile width or height. (default 5)
  * -s _projection_ or --projection=_projection_: Specify the projection of the input data. Currently supported are EPSG:4326 (WGS84, the default) and EPSG:3857 (Web Mercator).
+ * -k _bytes_ or --maximum-tile-bytes=_bytes_: Use the specified number of _bytes_ as the maximum compressed tile size instead of 500K.
 
 All internal math is done in terms of a 32-bit tile coordinate system, so 1/(2^32) of the size of Earth,
 or about 1cm, is the smallest distinguishable distance. If _maxzoom_ + _detail_ > 32, no additional

main.cpp

@@ -58,6 +58,7 @@ static int min_detail = 7;
 int quiet = 0;
 int geometry_scale = 0;
 double simplification = 1;
+size_t max_tile_size = 500000;
 
 int prevent[256];
 int additional[256];
@@ -1894,6 +1895,7 @@ int main(int argc, char **argv) {
 		{"additional", required_argument, 0, 'a'},
 		{"projection", required_argument, 0, 's'},
 		{"simplification", required_argument, 0, 'S'},
+		{"maximum-tile-bytes", required_argument, 0, 'k'},
 
 		{"exclude-all", no_argument, 0, 'X'},
 		{"force", no_argument, 0, 'f'},
@@ -1944,7 +1946,7 @@ int main(int argc, char **argv) {
 		}
 	}
 
-	while ((i = getopt_long(argc, argv, "n:l:z:Z:B:d:D:m:o:x:y:r:b:t:g:p:a:XfFqvPL:A:s:S:", long_options, NULL)) != -1) {
+	while ((i = getopt_long(argc, argv, "n:l:z:Z:B:d:D:m:o:x:y:r:b:t:g:p:a:XfFqvPL:A:s:S:k:", long_options, NULL)) != -1) {
 		switch (i) {
 		case 0:
 			break;
@@ -2123,6 +2125,10 @@ int main(int argc, char **argv) {
 			}
 			break;
 
+		case 'k':
+			max_tile_size = atoll(optarg);
+			break;
+
 		default: {
 			int width = 7 + strlen(argv[0]);
 			fprintf(stderr, "Usage: %s", argv[0]);

main.hpp

@@ -14,3 +14,5 @@ extern int quiet;
 
 extern size_t CPUS;
 extern size_t TEMP_FILES;
+
+extern size_t max_tile_size;

man/tippecanoe.1

@@ -102,6 +102,8 @@ compensate for the larger marker, or \-Bf\fInumber\fP to allow at most \fInumber
 \-b \fIpixels\fP or \-\-buffer=\fIpixels\fP: Buffer size where features are duplicated from adjacent tiles. Units are "screen pixels"\-\-1/256th of the tile width or height. (default 5)
 .IP \(bu 2
 \-s \fIprojection\fP or \-\-projection=\fIprojection\fP: Specify the projection of the input data. Currently supported are EPSG:4326 (WGS84, the default) and EPSG:3857 (Web Mercator).
+.IP \(bu 2
+\-k \fIbytes\fP or \-\-maximum\-tile\-bytes=\fIbytes\fP: Use the specified number of \fIbytes\fP as the maximum compressed tile size instead of 500K.
 .RE
 .PP
 All internal math is done in terms of a 32\-bit tile coordinate system, so 1/(2 of the size of Earth,

tile.cpp

@@ -900,6 +900,8 @@ void find_common_edges(std::vector<partial> &partials, int z, int line_detail, d
 		}
 	}
 
+	// Simplify each arc
+
 	std::vector<drawvec> simplified_arcs;
 
 	size_t count = 0;
@@ -924,6 +926,9 @@ void find_common_edges(std::vector<partial> &partials, int z, int line_detail, d
 		count++;
 	}
 
+	// If necessary, merge some adjacent polygons into some other polygons
+
+#if 0
 	for (size_t i = 0; i < partials.size(); i++) {
 		for (size_t j = 0; j < partials[i].arc_polygon.size(); j++) {
 			if (merge_candidates.count(-partials[i].arc_polygon[j]) > 0) {
@@ -1033,7 +1038,9 @@ void find_common_edges(std::vector<partial> &partials, int z, int line_detail, d
 			}
 		}
 	}
+#endif
 
+	// Turn the arc representations of the polygons back into standard polygon geometries
 
 	for (size_t i = 0; i < partials.size(); i++) {
 		if (partials[i].t == VT_POLYGON) {
@@ -1599,7 +1606,7 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 					}
 					line_detail++;  // to keep it the same when the loop decrements it
 					continue;
-				} else if (additional[A_INCREASE_GAMMA_AS_NEEDED]) {
+				} else if (additional[A_INCREASE_GAMMA_AS_NEEDED] && gamma < 10) {
 					if (gamma < 1) {
 						gamma = 1;
 					} else {
@@ -1619,21 +1626,21 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 
 			std::string compressed = tile.encode();
 
-			if (compressed.size() > 500000 && !prevent[P_KILOBYTE_LIMIT]) {
+			if (compressed.size() > max_tile_size && !prevent[P_KILOBYTE_LIMIT]) {
 				if (!quiet) {
-					fprintf(stderr, "tile %d/%u/%u size is %lld with detail %d, >500000    \n", z, tx, ty, (long long) compressed.size(), line_detail);
+					fprintf(stderr, "tile %d/%u/%u size is %lld with detail %d, >%zu    \n", z, tx, ty, (long long) compressed.size(), line_detail, max_tile_size);
 				}
 
 				if (prevent[P_DYNAMIC_DROP]) {
 					// The 95% is a guess to avoid too many retries
 					// and probably actually varies based on how much duplicated metadata there is
 
-					fraction = fraction * 500000 / compressed.size() * 0.95;
+					fraction = fraction * max_tile_size / compressed.size() * 0.95;
 					if (!quiet) {
 						fprintf(stderr, "Going to try keeping %0.2f%% of the features to make it fit\n", fraction * 100);
 					}
 					line_detail++;  // to keep it the same when the loop decrements it
-				} else if (additional[A_INCREASE_GAMMA_AS_NEEDED]) {
+				} else if (additional[A_INCREASE_GAMMA_AS_NEEDED] && gamma < 10) {
 					if (gamma < 1) {
 						gamma = 1;
 					} else {