App.js

import React, { Component } from "react";
import { Platform, StyleSheet, Text, View } from "react-native";
import MapView from "react-native-maps";

export default class App extends Component {
  render() {
    return (
      <View style={styles.container}>
        <MapView
          style={styles.map}
          initialRegion={{
            latitude: 37.78825,
            longitude: -122.4324,
            latitudeDelta: 0.0922,
            longitudeDelta: 0.0421
          }}
        >
          <MapView.Marker
            onPress={e => {
              console.log(e.nativeEvent);
            }}
            coordinate={{
              latitude: 37.78825,
              longitude: -122.4324
            }}
          />
        </MapView>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    position: "absolute",
    top: 0,
    left: 0,
    right: 0,
    bottom: 0,
    justifyContent: "flex-end",
    alignItems: "center"
  },
  map: {
    position: "absolute",
    top: 0,
    left: 0,
    right: 0,
    bottom: 0
  }
});