They were arranged to be physically and electrically compatible with the Wemos D1 Mini ESP8266: Reset pin RST is in the same place. All power pins are at the same places: 5V/VCC, 3.3V, and one of the ground pins. Serial communication lines up with UART TX/RX at the same places. ESP32 can perform I2C on most of its GPIO pins.
ESP8266 and BMP280 sensor example. BMP280 is an absolute barometric pressure sensor especially designed for mobile applications. The sensor module is housed in an extremely compact package. Its small dimensions and its low power consumption allow for the implementation in battery powered devices such as mobile phones, GPS modules or watches. The most widely used ESP8266 NodeMCU development boards are the ESP8266-12E NodeMCU Kit, the Wemos D1 Mini, and the ESP-01. We’ll show you the pinout for those boards. A pinout is like a map that shows which pin corresponds to which GPIO and its features. This way, you should know which GPIOs to use if you need to use SPI, I2C, ADC, or others. Like the one you can see on the screen is the ESP8266 d1 mini which is also known as Lolin Wemos D1 R2 Mini. You may also call this as the mini Nodemcu ESP8266 WiFi module. The only difference between the two boards are d1 mini is smaller in size and it has less IO pins. The programming is 100% the same.