map组件中roads类型地图无法正常显示，但其他类型地图可以正常显示
你是中国人，所以有些路道不会被地图正确显示。
问题是，地图元件不是使用高德地图，而是用美国的开放街道地图。由于资料大都是关于欧美地区，所以有可能缺少中国的一些街道。 我不知道MIT是否会解决这个问题，但是由于地图的提供商不是MIT，所以有可能修不了。
你可以用其他方法试一下。论坛里有关于使用谷歌地图的文章，但是是用英文写的，而且谷歌地图在内地用不了（除非你有VPN）。
祝你好运。
OpenStreetMap might not include some roads in the mainland. I've tried that myself when I was there. You might want to switch to an alternative.
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This is unusual. The Road Map type 'always displays' You say that the Aerial and Terrain maps display properly for you. The Aerial and Terrain maps do not usually display at zoom values of 8 and higher because the maps are not available at the higher magnifications everywhere as @gordonlu310 mentioned. Try a zoom of 5. 
Please post an example of how your app displays a Road, an Aerial and a Terrain map so we can determine what might be the problem. Thank you.
The Map component uses the OpenStreetMap map tile set. It does not use the Google Map Tiles.
This is an OpenStreetMap of Bejing .
All the roads displayed here should also display using the Map component. If a Road you expect to see does not display it is because it is either not available or the information is blocked.
Part of the same map centered at 39.9190,116.5454 shown on an app:
If I use Aerial or Terrain, there are no map tiles to display. You can see Roads but not Aerial or Terrain. 
On an emulator the Aerial and Terrain do not display however they both display on a real device at a zoom of 5.
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I live in Mainland of China, I never used Map component, since it's not working here. (not fault of App Inventor, but the policy of China)
I can use Bing map, or Tencent Map, or Baidu Map.
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Kevin, can you confirm this does not work in China please. I know Google Maps is blocked there but OSM used to work there.
Beijing.aia (1.1 KB)
Thanks! OSM evidently no longer works in mainland China as the OSM tiles are blocked.
在我开始使用MAP组件时的几天时间里，roads类型地图是可以正常显示的，后来过了几天就突然不能正常显示了，但其他两种类型地图还可以正常显示。
在最近几天才不提供服务的吗？
我可以看到Aerial and Terrain 类型地图，不能看到roads类型地图
Thank you. Aerial and Terrain are probably not being blocked but due to China policy Road maps are Blocked.
Kevinkun says he uses
You may be able to use Bing the with a WebViewer with a url like' Bing Maps - Directions, trip planning, traffic cameras & more '
or using your LocationSensor to supply the latitude and longitude. Here is a tutorial showing how to do that with OSM (which you cannot probably do in China). Use similar code as shown .
https://groups.google.com/g/mitappinventortest/c/gGAeQN3r_fg/m/Dc8PY5HrAwAJ