diff --git a/Cargo.lock b/Cargo.lock
index 5bcf5ed..02969fb 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -10,7 +10,7 @@ dependencies = [
 
 [[package]]
 name = "arrayref"
-version = "0.3.5"
+version = "0.3.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -18,8 +18,8 @@ name = "atty"
 version = "0.2.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "hermit-abi 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.66 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hermit-abi 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.68 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -28,8 +28,8 @@ name = "bincode"
 version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
+ "byteorder 1.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.105 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -39,17 +39,9 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "byteorder"
-version = "1.3.2"
+version = "1.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
-[[package]]
-name = "c2-chacha"
-version = "0.2.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "ppv-lite86 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "cfg-if"
 version = "0.1.10"
@@ -64,6 +56,7 @@ dependencies = [
  "atty 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "strsim 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "term_size 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "textwrap 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "unicode-width 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "vec_map 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -75,7 +68,7 @@ version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.66 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.68 (registry+https://github.com/rust-lang/crates.io-index)",
  "wasi 0.9.0+wasi-snapshot-preview1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -89,10 +82,10 @@ dependencies = [
 
 [[package]]
 name = "hermit-abi"
-version = "0.1.6"
+version = "0.1.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "libc 0.2.66 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.68 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -104,29 +97,33 @@ name = "ironsea_index_hashmap"
 version = "0.1.0"
 dependencies = [
  "ironsea_index 0.1.0",
- "serde 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.105 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "ironsea_index_sfc_dbc"
 version = "0.1.0"
 dependencies = [
- "arrayref 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "arrayref 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "ironsea_index 0.1.0",
- "ironsea_store 0.1.0",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.105 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
-name = "ironsea_store"
-version = "0.1.0"
+name = "itoa"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
-name = "itoa"
-version = "0.4.4"
+name = "kernel32-sys"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
 
 [[package]]
 name = "lazy_static"
@@ -135,7 +132,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "libc"
-version = "0.2.66"
+version = "0.2.68"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -151,7 +148,7 @@ name = "memmap"
 version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "libc 0.2.66 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.68 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -159,18 +156,19 @@ dependencies = [
 name = "mercator_data_generator"
 version = "0.1.0"
 dependencies = [
+ "clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "mercator_db 0.1.0",
  "rand 0.7.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_json 1.0.44 (registry+https://github.com/rust-lang/crates.io-index)",
- "structopt 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.105 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.48 (registry+https://github.com/rust-lang/crates.io-index)",
+ "structopt 0.3.12 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "mercator_db"
 version = "0.1.0"
 dependencies = [
- "arrayref 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "arrayref 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "ironsea_index 0.1.0",
  "ironsea_index_hashmap 0.1.0",
@@ -178,8 +176,8 @@ dependencies = [
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "memmap 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_json 1.0.44 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.105 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.48 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -189,31 +187,31 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "proc-macro-error"
-version = "0.4.4"
+version = "0.4.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "proc-macro-error-attr 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "proc-macro2 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "rustversion 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro-error-attr 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro2 1.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.16 (registry+https://github.com/rust-lang/crates.io-index)",
+ "version_check 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "proc-macro-error-attr"
-version = "0.4.3"
+version = "0.4.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "proc-macro2 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "rustversion 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.13 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn-mid 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro2 1.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.16 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn-mid 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "version_check 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.7"
+version = "1.0.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -221,10 +219,10 @@ dependencies = [
 
 [[package]]
 name = "quote"
-version = "1.0.2"
+version = "1.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "proc-macro2 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro2 1.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -233,18 +231,18 @@ version = "0.7.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "getrandom 0.1.14 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.66 (registry+https://github.com/rust-lang/crates.io-index)",
- "rand_chacha 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.68 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand_chacha 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand_core 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand_hc 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "rand_chacha"
-version = "0.2.1"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "c2-chacha 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ppv-lite86 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand_core 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -264,47 +262,37 @@ dependencies = [
  "rand_core 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "rustversion"
-version = "1.0.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "proc-macro2 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.13 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "ryu"
-version = "1.0.2"
+version = "1.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "serde"
-version = "1.0.104"
+version = "1.0.105"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "serde_derive 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.105 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.104"
+version = "1.0.105"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "proc-macro2 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro2 1.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.16 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "serde_json"
-version = "1.0.44"
+version = "1.0.48"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "itoa 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "ryu 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.104 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itoa 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ryu 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.105 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -314,43 +302,54 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "structopt"
-version = "0.3.7"
+version = "0.3.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "structopt-derive 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "structopt-derive 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "structopt-derive"
-version = "0.4.0"
+version = "0.4.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "heck 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "proc-macro-error 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "proc-macro2 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro-error 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro2 1.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.16 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "syn"
-version = "1.0.13"
+version = "1.0.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "proc-macro2 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro2 1.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "syn-mid"
-version = "0.4.0"
+version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "proc-macro2 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 1.0.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro2 1.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 1.0.16 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "term_size"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.68 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -358,6 +357,7 @@ name = "textwrap"
 version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
+ "term_size 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "unicode-width 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -381,11 +381,21 @@ name = "vec_map"
 version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "version_check"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "wasi"
 version = "0.9.0+wasi-snapshot-preview1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "winapi"
+version = "0.2.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "winapi"
 version = "0.3.8"
@@ -395,6 +405,11 @@ dependencies = [
  "winapi-x86_64-pc-windows-gnu 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "winapi-build"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "winapi-i686-pc-windows-gnu"
 version = "0.4.0"
@@ -407,47 +422,50 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [metadata]
 "checksum ansi_term 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ee49baf6cb617b853aa8d93bf420db2383fab46d314482ca2803b40d5fde979b"
-"checksum arrayref 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)" = "0d382e583f07208808f6b1249e60848879ba3543f57c32277bf52d69c2f0f0ee"
+"checksum arrayref 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "a4c527152e37cf757a3f78aae5a06fbeefdb07ccc535c980a3208ee3060dd544"
 "checksum atty 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)" = "d9b39be18770d11421cdb1b9947a45dd3f37e93092cbf377614828a319d5fee8"
 "checksum bincode 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "5753e2a71534719bf3f4e57006c3a4f0d2c672a4b676eec84161f763eca87dbf"
 "checksum bitflags 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
-"checksum byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "a7c3dd8985a7111efc5c80b44e23ecdd8c007de8ade3b96595387e812b957cf5"
-"checksum c2-chacha 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "214238caa1bf3a496ec3392968969cab8549f96ff30652c9e56885329315f6bb"
+"checksum byteorder 1.3.4 (registry+https://github.com/rust-lang/crates.io-index)" = "08c48aae112d48ed9f069b33538ea9e3e90aa263cfa3d1c24309612b1f7472de"
 "checksum cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)" = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
 "checksum clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5067f5bb2d80ef5d68b4c87db81601f0b75bca627bc2ef76b141d7b846a3c6d9"
 "checksum getrandom 0.1.14 (registry+https://github.com/rust-lang/crates.io-index)" = "7abc8dd8451921606d809ba32e95b6111925cd2906060d2dcc29c070220503eb"
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diff --git a/Cargo.toml b/Cargo.toml
index 509a386..6d3f46f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -19,11 +19,15 @@ license = "MIT"
 include = ["Cargo.toml", "README.md", "LICENSE", "ACKNOWLEDGEMENTS", "src/**/*.rs"]
 
 [dependencies]
+mercator_db = "^0.1"
+rand = "^0.7"
+
 serde = { version = "^1.0", features = ["derive"] }
 serde_json = "^1.0"
-rand = "^0.7"
+
+# Online help & argument parsing
+clap = {version = "2.33.0", features = ["wrap_help"]}
 structopt = "^0.3"
-mercator_db = "^0.1"
 
 [workspace]
 
diff --git a/src/main.rs b/src/main.rs
index 6b7ef85..f4af4d6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -117,13 +117,14 @@ fn generate_data(nb_points: usize, factor: usize, rng: &mut ThreadRng, die: &Uni
     store(format!("{}k.objects", nb_points).as_str(), objects);
 }
 
+/// Tool to generate test data for Mercator, a spatial index.
 #[derive(StructOpt, Debug)]
 struct Opt {
-    /// Number of ids per positions generated
+    /// Number of ids per positions to generate.
     #[structopt(long, short)]
     factor: Option<usize>,
 
-    /// List of Number of features to be generated.
+    /// List of number of features to generate, each stored in its own file.
     datasets: Vec<usize>,
 }