diff --git a/index.js b/index.js
index 39a1993..7f5a39f 100644
--- a/index.js
+++ b/index.js
@@ -6,7 +6,7 @@ var crypto = require('crypto');
 module.exports = abaculus;
 
 function abaculus(arg, callback) {
-    var z = arg.zoom || 1,
+    var z = arg.zoom || 0,
         s = arg.scale || 1,
         center = arg.center || null,
         bbox = arg.bbox || null,
@@ -16,17 +16,21 @@ function abaculus(arg, callback) {
         limit = arg.limit || 19008,
         tileSize = arg.tileSize || 256;
 
-    if (!getTile) return callback(new Error('Invalid function for getting tiles'));
+    if (!getTile) return callback(new Error('Invalid function for getting tiles.'));
 
     if (center) {
         // get center coordinates in px from lng,lat
-        center = abaculus.coordsFromCenter(z, s, center, limit, tileSize);
+        center = abaculus.coordsFromCenter(z, s, center, tileSize);
     } else if (bbox) {
         // get center coordinates in px from [w,s,e,n] bbox
-        center = abaculus.coordsFromBbox(z, s, bbox, limit, tileSize);
+        center = abaculus.coordsFromBbox(z, s, bbox, tileSize);
     } else {
         return callback(new Error('No coordinates provided.'));
     }
+
+    if (center.w <= 0 || center.h <= 0) return callback(new Error('Incorrect coordinates.'));
+    if (center.w >= limit || center.h >= limit) return callback(new Error('Desired image is too large.'));
+
     // generate list of tile coordinates center
     var coords = abaculus.tileList(z, s, center, tileSize);
 
@@ -34,35 +38,31 @@ function abaculus(arg, callback) {
     abaculus.stitchTiles(coords, format, quality, getTile, callback);
 }
 
-abaculus.coordsFromBbox = function(z, s, bbox, limit, tileSize) {
-    var sm = new SphericalMercator({ size: tileSize * s });
+abaculus.coordsFromBbox = function(z, s, bbox, tileSize) {
+    var sm = new SphericalMercator({ size: (tileSize || 256) * s });
     var topRight = sm.px([bbox[2], bbox[3]], z),
         bottomLeft = sm.px([bbox[0], bbox[1]], z);
     var center = {};
     center.w = topRight[0] - bottomLeft[0];
     center.h = bottomLeft[1] - topRight[1];
 
-    if (center.w <= 0 || center.h <= 0) throw new Error('Incorrect coordinates');
-
     var origin = [topRight[0] - center.w / 2, topRight[1] + center.h / 2];
     center.x = origin[0];
     center.y = origin[1];
-    center.w = Math.round(center.w * s);
-    center.h = Math.round(center.h * s);
+    center.w = Math.round(center.w);
+    center.h = Math.round(center.h);
 
-    if (center.w >= limit || center.h >= limit) throw new Error('Desired image is too large.');
     return center;
 };
 
-abaculus.coordsFromCenter = function(z, s, center, limit, tileSize) {
-    var sm = new SphericalMercator({ size: tileSize * s });
+abaculus.coordsFromCenter = function(z, s, center, tileSize) {
+    var sm = new SphericalMercator({ size: (tileSize || 256) * s });
     var origin = sm.px([center.x, center.y], z);
     center.x = origin[0];
     center.y = origin[1];
     center.w = Math.round(center.w * s);
     center.h = Math.round(center.h * s);
 
-    if (center.w >= limit || center.h >= limit) throw new Error('Desired image is too large.');
     return center;
 };
 
@@ -78,8 +78,8 @@ abaculus.tileList = function(z, s, center, tileSize) {
     var ts = Math.round(size * s);
 
     var centerCoordinate = {
-        column: x / size,
-        row: y / size,
+        column: x / ts,
+        row: y / ts,
         zoom: z
     };
 
@@ -112,7 +112,7 @@ abaculus.tileList = function(z, s, center, tileSize) {
     }
 
     var tl = floorObj(pointCoordinate({x: 0, y:0}));
-    var br = floorObj(pointCoordinate(dimensions));
+    var br = floorObj(pointCoordinate({ x: dimensions.x - 1, y: dimensions.y - 1 }));
     var coords = {};
     coords.tiles = [];
     var tileCount = (br.column - tl.column + 1) * (br.row - tl.row + 1);
@@ -131,7 +131,10 @@ abaculus.tileList = function(z, s, center, tileSize) {
                 Math.pow(2,c.zoom) + c.column :
                 c.column % Math.pow(2,c.zoom);
 
-            if (c.row < 0) continue;
+            c.row = c.row < 0 ?
+                Math.pow(2, c.zoom) + c.row :
+                c.row % Math.pow(2, c.zoom);
+
             coords.tiles.push({
                 z: c.zoom,
                 x: c.column,
diff --git a/test/test.js b/test/test.js
index 46a36dd..e745e39 100644
--- a/test/test.js
+++ b/test/test.js
@@ -11,7 +11,8 @@ var zoom = 5,
     y = 4096,
     quality = 256,
     format = 'png',
-    limit = 19008;
+    limit = 19008,
+    tileSize = 256;
 
 
 // fixtures
@@ -25,27 +26,27 @@ describe('Get center from bbox', function() {
     it('should fail if (x1, y1) and (x2,y2) are equal', function(done) {
         var bbox = [0, 0, 0, 0];
 
-        assert.throws( function() {
-            printer.coordsFromBbox(zoom, scale, bbox, limit);
-        }, /Incorrect coordinates/);
+        var center = printer.coordsFromBbox(zoom, scale, bbox, tileSize);
+        assert(center.w <= 0 || center.h <= 0, 'Incorrect coordinates')
+
         done();
     });
     it('should fail if the image is too large', function(done) {
         var bbox = [-60, -60, 60, 60];
 
-        assert.throws( function() {
-            printer.coordsFromBbox(7, 2, bbox, limit);
-        }, /Desired image is too large./);
+        var center = printer.coordsFromBbox(7, 2, bbox, tileSize);
+        assert(center.w >= limit || center.h >= limit, 'Desired image is too large')
+
         done();
     });
     it('should return the correct coordinates', function(done) {
         var bbox = [-60, -60, 60, 60];
 
-        var center = printer.coordsFromBbox(zoom, scale, bbox, limit);
-        assert.deepEqual(center.w, 10920);
+        var center = printer.coordsFromBbox(zoom, scale, bbox, tileSize);
+        assert.deepEqual(center.w, 10922);
         assert.deepEqual(center.h, 13736);
-        assert.deepEqual(center.x, x);
-        assert.deepEqual(center.y, y);
+        assert.deepEqual(center.x, 16384);
+        assert.deepEqual(center.y, 16384);
         done();
     });
 });
@@ -58,9 +59,10 @@ describe('get coordinates from center', function() {
             w: 4752,
             h: 4752
         };
-        assert.throws( function() {
-            printer.coordsFromCenter(zoom, scale, center, limit);
-        }, /Desired image is too large./);
+
+        var center = printer.coordsFromCenter(zoom, scale, center, tileSize);
+        assert(center.w >= limit || center.h >= limit, 'Desired image is too large')
+
         done();
     });
     it('should return correct origin coords', function(done) {
@@ -70,9 +72,9 @@ describe('get coordinates from center', function() {
             w: 800,
             h: 800
         };
-        center = printer.coordsFromCenter(zoom, scale, center, limit);
-        assert.equal(center.x, x);
-        assert.equal(center.y, 3631);
+        var center2 = printer.coordsFromCenter(zoom, scale, center, tileSize);
+        assert.equal(center2.x, 16384);
+        assert.equal(center2.y, 14525);
         done();
     });
 });
@@ -82,13 +84,13 @@ describe('create list of tile coordinates', function() {
 
     var expectedCoords = {
         tiles: [
-            { z: 5, x: 15, y: 15, px: -112, py: -108 },
-            { z: 5, x: 15, y: 16, px: -112, py: 916 },
-            { z: 5, x: 16, y: 15, px: 912, py: -108 },
-            { z: 5, x: 16, y: 16, px: 912, py: 916 }
+            { z: 5, x: 3, y: 3, px: -112, py: -108 },
+            { z: 5, x: 3, y: 4, px: -112, py: 916 },
+            { z: 5, x: 4, y: 3, px: 912, py: -108 },
+            { z: 5, x: 4, y: 4, px: 912, py: 916 }
         ],
         dimensions: { x: 1824, y: 1832 },
-        center: { row: 16, column: 16, zoom: 5 },
+        center: { row: 4, column: 4, zoom: 5 },
         scale: 4
     };
     it('should return a tiles object with correct coords', function(done) {