1.index.wxml

<map class="map"
  longitude="{{myLongitude}}"
  latitude="{{myLatitude}}"
  scale="{{mapScale}}"
  controls="{{controls}}"
  bindcontroltap="controltap"
  markers="{{markers}}"
  bindmarkertap="markertap"
  polyline="{{polyline}}"
  bindregionchange="regionchange"
  show-location
  style="width: 100%; height: {{mapHeight}}px;">
</map>

<canvas class="{{showHeader ? 'canvas' : 'canvasHide'}}" canvas-id="myCanvas">
</canvas>

2.index.wxss

.canvas {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 240rpx;
  display: block;
  background-color: #ff0000;
}

.canvasHide {
  display: none;
}

3.Postscript

any question comment below,i will reponse you.