qmk_firmware/keyboards/handwired/jotpad16/keymaps/default/keymap.c

// This is the canonical layout file for the Quantum project. If you want to add another keyboard,
// this is the style you want to emulate.

#include QMK_KEYBOARD_H

extern keymap_config_t keymap_config;

// Each layer gets a name for readability, which is then used in the keymap matrix below.
// The underscores don't mean anything - you can have a layer called STUFF or any other name.
// Layer names don't all need to be of the same length, obviously, and you can also skip them
// entirely and just use numbers.

#define _NUMPAD 0

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {

/* Numpad
 * +-------+-------+-------+-------+
 * |   7   |   8   |   9   |   -   |
 * +-------+-------+-------+-------+
 * |   4   |   5   |   6   |   +   |
 * +-------+-------+-------+-------+
 * |   1   |   2   |   3   | enter |
 * +-------+-------+-------+-------+
 * |   0   |   .   |   /   |   *   |
 * +-------+-------+-------+-------+
 */
[_NUMPAD] = LAYOUT_ortho_4x4( 
    KC_P7,  KC_P8,  KC_P9,  KC_MINS,
    KC_P4,  KC_P5,  KC_P6,  KC_PLUS,
    KC_P1,  KC_P2,  KC_P3,  KC_PENT,
    KC_P0,  KC_PDOT,KC_PSLS,KC_ASTR 
),
};