1 00:00:01,520 --> 00:00:07,589 Hi and welcome again to yet another lecture on web mapping with Python and 2 00:00:07,589 --> 00:00:15,210 Folium This is the map we built this far, and it contains a base layer, 3 00:00:15,210 --> 00:00:23,910 a polygon layer, and a marker layer. This is our code. Now what I want to do in this 4 00:00:23,910 --> 00:00:29,310 lecture, I want to implement a feature that allows me to turn the custom layers 5 00:00:29,310 --> 00:00:34,700 on and off. With custom layers I mean the polygon layer and the marker or layer 6 00:00:34,700 --> 00:00:39,290 because it's not possible to turn off the base map at least as far as I know. 7 00:00:39,290 --> 00:00:45,320 And it wouldn't make sense to turn off the base layer, you don't want a blank page. 8 00:00:45,320 --> 00:00:53,399 So let's see how to do that the key feature here is the layer control class of 9 00:00:53,399 --> 00:01:00,570 the folium module which can be added like this. You want to point to the map 10 00:01:00,570 --> 00:01:06,409 object, then you want to add a child, so layer control is added as a child. 11 00:01:06,409 --> 00:01:20,189 Folium.LayerControl. Now this will not work, but I still want to execute this so 12 00:01:20,189 --> 00:01:26,340 that you don't make this mistake later on. So let me reload the page. You only 13 00:01:26,340 --> 00:01:33,020 see the base map here, no layers at all. The reason this doesn't work is that 14 00:01:33,020 --> 00:01:38,640 when you added layer control to the map, you still hadn't added the feature 15 00:01:38,640 --> 00:01:46,710 group which is an object that contains the JSON layer and the marker 16 00:01:46,710 --> 00:01:52,530 layer, so basically layer control will be looking for the feature group added to 17 00:01:52,530 --> 00:01:57,990 the map, but it doesn't find it at this point, therefore things are messed up. 18 00:01:57,990 --> 00:02:04,439 So it's important to put that after you have added the feature group layer to 19 00:02:04,439 --> 00:02:16,530 the map right here. Save, and execute again, reload the map, and you see the 20 00:02:16,530 --> 00:02:24,030 layers there and you see this box here, mapboxbright, this is about the 21 00:02:24,030 --> 00:02:32,069 base map and you cannot turn this off, and you also have this my map item here 22 00:02:32,069 --> 00:02:36,930 of the layer control panel, so this is the layer control panel and you can turn 23 00:02:36,930 --> 00:02:43,379 on and off of this layer, but as you see this is turning off and on both the 24 00:02:43,379 --> 00:02:48,140 polygon and the point layer at the same time which is something you don't want. 25 00:02:48,140 --> 00:02:54,569 So we go ahead and change that and I'll explain why this happens so this is 26 00:02:54,569 --> 00:03:00,629 happening because you know layer control what it does it looks for 27 00:03:00,629 --> 00:03:07,470 objects added to map with add child like here so you have added a child, and you 28 00:03:07,470 --> 00:03:12,480 have added only one child to the map object therefore layer control will 29 00:03:12,480 --> 00:03:19,230 consider that object as one single item of the layer control panel, but that 30 00:03:19,230 --> 00:03:24,930 feature group object it contains the circle markers but it 31 00:03:24,930 --> 00:03:29,940 also contains the GeoJSON layer. Therefore you need to change your 32 00:03:29,940 --> 00:03:35,459 strategy here. So how can you do that? There may be different ways. One way is 33 00:03:35,459 --> 00:03:43,680 to actually create a feature group for volcanos, let's call it fgv, so you add 34 00:03:43,680 --> 00:03:49,680 fgv here and then you want another feature group. Let me copy this line 35 00:03:49,680 --> 00:03:52,849 paste it here. You want another feature group for 36 00:03:55,700 --> 00:04:04,010 population. Let's call this population. Let's call this volcanoes like that. 37 00:04:04,010 --> 00:04:15,890 Change the variable name fgp, fgp here. Okay. Fgv there, again. 38 00:04:17,190 --> 00:04:26,670 Add another child which has to be fgp for population. Yeah, now everything looks 39 00:04:26,670 --> 00:04:36,190 good, so let's see if layer control will be able to read these two feature groups 40 00:04:36,190 --> 00:04:49,540 now. Okay, go and reload. The map looks fine. Volcanoes, working well, population 41 00:04:49,540 --> 00:04:59,860 too, so everything is working fine. This is the map. And yeah, if you were able to build 42 00:04:59,860 --> 00:05:08,800 this as I did, then good job! You can also choose not to use feature groups 43 00:05:08,800 --> 00:05:17,530 actually, so you could have added GeoJSON to the map directly, however for 44 00:05:17,530 --> 00:05:23,740 this case for vocals where you are adding, you are executing the add child 45 00:05:23,740 --> 00:05:29,680 method multiple times, in that case you would have a while layer for every 46 00:05:29,680 --> 00:05:37,630 volcano, so you'd have added 62 children to your map object if you did map 47 00:05:37,630 --> 00:05:45,540 without feature group here, so that means in this control panel here you'd have 62 48 00:05:45,540 --> 00:05:52,180 entries, 62 layers, and that's not what we want, so feature group comes in handy in here. 49 00:05:52,180 --> 00:05:58,900 For volcanoes it is necessary, but for GeoJSON you could have used map 50 00:05:58,900 --> 00:06:05,340 here and everything would be fine, but for consistency it's good to add both to 51 00:06:05,340 --> 00:06:13,930 particular, to specific feature groups. Volcanoes here, and population here, so this 52 00:06:13,930 --> 00:06:20,130 is the code, and I hope you enjoyed this program, and feel free to ask questions. 53 00:06:20,130 --> 00:06:23,000 And I'll talk to you later on. See you!