Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated:
1
00:00:00,000 --> 00:00:03,690
Scale on a web map is a little different than it would be on a paper map.
2
00:00:03,690 --> 00:00:06,845
So, let's have a look at scale in relation to web mapping.
3
00:00:06,845 --> 00:00:15,075
Okay. So, here we have a zoomed out map of the entire world in ArcGIS Online.
4
00:00:15,075 --> 00:00:18,200
This is actually referred to as zoom level zero.
5
00:00:18,200 --> 00:00:20,810
What this is, is that it's almost the entire world.
6
00:00:20,810 --> 00:00:22,885
It's a little bit of the poles that are cut off,
7
00:00:22,885 --> 00:00:29,640
but almost the entire world is found inside this one square,
8
00:00:29,640 --> 00:00:33,680
that's 250 pixels wide by 250 pixels high.
9
00:00:33,680 --> 00:00:35,900
So, it's a perfect square which happens to be very
10
00:00:35,900 --> 00:00:39,390
useful for making web maps as you'll see in a second.
11
00:00:39,390 --> 00:00:46,950
If I zoom in, what's just happened here is that the map scale has gotten larger.
12
00:00:46,950 --> 00:00:48,335
In fact it's doubled.
13
00:00:48,335 --> 00:00:51,500
So, that the size of the map that we're looking at has doubled,
14
00:00:51,500 --> 00:00:54,365
and so we've increased the map scale.
15
00:00:54,365 --> 00:00:57,070
If I zoom in, again,
16
00:00:57,070 --> 00:01:00,620
we've gone to another zoom level or scale level.
17
00:01:00,620 --> 00:01:03,150
That's the terminology that's used for web mapping,
18
00:01:03,150 --> 00:01:07,030
and the map scale has gotten larger again and it's doubled again.
19
00:01:07,030 --> 00:01:10,105
So, this is zoom level three.
20
00:01:10,105 --> 00:01:15,720
We can continue to zoom in here and see more and more detail.
21
00:01:15,850 --> 00:01:20,910
If we zoom in all the way to the highest or largest scale map,
22
00:01:20,910 --> 00:01:22,375
which is zoom level 20,
23
00:01:22,375 --> 00:01:24,670
you can see individual buildings,
24
00:01:24,670 --> 00:01:25,975
the footprints of buildings,
25
00:01:25,975 --> 00:01:30,265
and you may recognize this or may not depending on if you've been there before,
26
00:01:30,265 --> 00:01:32,720
it's Buckingham Palace in London England.
27
00:01:32,720 --> 00:01:34,400
So, if you ever have a chance to go there,
28
00:01:34,400 --> 00:01:36,980
it's an absolutely beautiful impressive building.
29
00:01:36,980 --> 00:01:38,610
I took a tour through there one time.
30
00:01:38,610 --> 00:01:41,795
I think it's open to the public, just in the summer when the Queen is not in residence,
31
00:01:41,795 --> 00:01:43,350
and I would recommend it,
32
00:01:43,350 --> 00:01:44,880
it's really interesting to go through.
33
00:01:44,880 --> 00:01:49,040
Anyway, so that is the highest level of zooming in,
34
00:01:49,040 --> 00:01:53,035
if you want or the largest map scale that's available in a web map.
35
00:01:53,035 --> 00:01:54,550
Just to give you a sense of,
36
00:01:54,550 --> 00:01:56,015
so, we went from the entire world,
37
00:01:56,015 --> 00:02:00,625
down to one building which is incredibly impressive to say the least.
38
00:02:00,625 --> 00:02:02,410
So, up until now,
39
00:02:02,410 --> 00:02:06,655
I've been talking about maps as though they're static like you would have on a paper map.
40
00:02:06,655 --> 00:02:09,290
But it's a little bit different when you're talking about a web map,
41
00:02:09,290 --> 00:02:13,680
because that might be seen on a big screen or a desktop computer,
42
00:02:13,680 --> 00:02:15,250
it might be on a tablet,
43
00:02:15,250 --> 00:02:17,300
it might be on a phone.
44
00:02:17,300 --> 00:02:19,785
What's interesting about this is that,
45
00:02:19,785 --> 00:02:23,565
the area that's being mapped here on this screen is the same.
46
00:02:23,565 --> 00:02:27,465
In other words, they're all showing the same amount of the world.
47
00:02:27,465 --> 00:02:31,710
Right? But the size of the map that's being used to show it is different.
48
00:02:31,710 --> 00:02:35,835
So, this is actually a larger scale map here,
49
00:02:35,835 --> 00:02:38,775
and this is a smaller scale map here.
50
00:02:38,775 --> 00:02:42,950
Because remember, the scale is just the ratio of the map distance to the ground distance,
51
00:02:42,950 --> 00:02:46,090
and so the ground distance here in a way is the same,
52
00:02:46,090 --> 00:02:47,775
that's what we're holding constant is that,
53
00:02:47,775 --> 00:02:52,540
the distance from this side of the map to the other on the ground is the same,
54
00:02:52,540 --> 00:02:55,220
but the distance on the map itself is different
55
00:02:55,220 --> 00:02:58,780
depending on the screen that's being used to display it.
56
00:02:58,780 --> 00:03:01,370
So, you may notice when you're looking at a web map,
57
00:03:01,370 --> 00:03:05,390
that they don't include a representative fraction on those maps,
58
00:03:05,390 --> 00:03:07,280
because it would constantly be changing and they'd
59
00:03:07,280 --> 00:03:09,439
have to keep recalculating it all the time,
60
00:03:09,439 --> 00:03:12,920
and it would have to know the size of the display that's being used and so on,
61
00:03:12,920 --> 00:03:15,270
so, instead what they just do to keep things simple is,
62
00:03:15,270 --> 00:03:17,665
they put a bar scale on the map, and so,
63
00:03:17,665 --> 00:03:21,095
if you are looking at that on a larger screen,
64
00:03:21,095 --> 00:03:22,750
the same-sized area that is,
65
00:03:22,750 --> 00:03:27,485
the bar scale will automatically be larger along with the rest of the map,
66
00:03:27,485 --> 00:03:30,895
and so that will still be representative of the scale of that map.
67
00:03:30,895 --> 00:03:31,990
If you're on a smaller screen,
68
00:03:31,990 --> 00:03:33,520
the scale bar will get smaller,
69
00:03:33,520 --> 00:03:37,040
and so that's kind of a trick they use in order to be able to
70
00:03:37,040 --> 00:03:40,570
actually show you what the scale is in terms of distances on the ground,
71
00:03:40,570 --> 00:03:44,350
but they're not showing you that fractional version of the scale.
72
00:03:44,350 --> 00:03:48,130
So, this is just a different way of thinking about scale is on the top part here,
73
00:03:48,130 --> 00:03:51,500
we're keeping the distance on the map the same,
74
00:03:51,500 --> 00:03:54,200
and changing the size of the map itself,
75
00:03:54,200 --> 00:03:55,620
and on the bottom here,
76
00:03:55,620 --> 00:03:59,945
we're keeping the size of the map the same in the distance on the ground is changing.
77
00:03:59,945 --> 00:04:01,370
So, either way, it's the same thing.
78
00:04:01,370 --> 00:04:06,780
Just remember it's just a ratio of map distance to ground distance,
79
00:04:06,780 --> 00:04:08,790
and so you're just trying to figure out,
80
00:04:08,790 --> 00:04:11,615
what is it I'm looking at and what's the relationship.
81
00:04:11,615 --> 00:04:15,570
I think it's useful to know a little bit about web mapping,
82
00:04:15,570 --> 00:04:17,040
this does relate to scale,
83
00:04:17,040 --> 00:04:18,970
but also just about like, how does this work?
84
00:04:18,970 --> 00:04:20,060
Why is it set up that way?
85
00:04:20,060 --> 00:04:21,320
Because I think most of,
86
00:04:21,320 --> 00:04:23,390
all of us use web maps a lot,
87
00:04:23,390 --> 00:04:26,040
so, you might as well have a sense of like, well, how does this work?
88
00:04:26,040 --> 00:04:27,635
So let's have a quick look.
89
00:04:27,635 --> 00:04:33,710
So, here I'm showing you the entire world in one square which is at zoom level zero.
90
00:04:33,710 --> 00:04:37,375
So, that's as far out as we can zoom in a web map.
91
00:04:37,375 --> 00:04:44,005
When that's represented on our browser or whatever app that we're using,
92
00:04:44,005 --> 00:04:46,650
if we're at the correct resolution,
93
00:04:46,650 --> 00:04:51,945
then that's a 256 pixel by 256 pixel size image.
94
00:04:51,945 --> 00:04:54,660
So, literally 256 pixels,
95
00:04:54,660 --> 00:04:56,545
that way and that way.
96
00:04:56,545 --> 00:04:59,980
Pixel by the way is a short form for picture elements.
97
00:04:59,980 --> 00:05:01,660
I don't know if you knew that little trivia for you.
98
00:05:01,660 --> 00:05:03,740
So, that's where the word pixel comes from.
99
00:05:03,740 --> 00:05:06,940
So, there's 256 dots on each of
100
00:05:06,940 --> 00:05:11,510
the axes that are being used to make up this image of the map.
101
00:05:12,320 --> 00:05:18,490
So, this 256 by 256 image is referred to as a map tiles.
102
00:05:18,490 --> 00:05:23,460
So, we can and show the entire world in one map tile at zoom level zero.
103
00:05:23,510 --> 00:05:26,435
If we go to zoom level one,
104
00:05:26,435 --> 00:05:30,570
we've doubled the size of our image of that world,
105
00:05:30,570 --> 00:05:36,380
and so now we have 512 pixels to work with on both axes,
106
00:05:36,380 --> 00:05:38,840
and we have four map tiles.
107
00:05:38,840 --> 00:05:45,110
So, each of these map tiles is still 256 pixels this way and that way,
108
00:05:45,110 --> 00:05:48,710
but since we have four tiles that's 512 pixels
109
00:05:48,710 --> 00:05:52,760
all the way from top to bottom and 512 from left to right.
110
00:05:52,760 --> 00:05:58,395
So, now we've doubled the number of pixels that are needed in both directions,
111
00:05:58,395 --> 00:05:59,865
so that's actually quadrupling,
112
00:05:59,865 --> 00:06:01,895
the number of pixels in total that we need
113
00:06:01,895 --> 00:06:04,480
quadrupling the amount of data that needs to be stored,
114
00:06:04,480 --> 00:06:07,010
as we increase the mass scale.
115
00:06:07,010 --> 00:06:13,050
When a company like Esri or Google or whomever decides to make a web map,
116
00:06:13,050 --> 00:06:15,799
what they're doing is, you're saying, Okay we're going to take the entire world,
117
00:06:15,799 --> 00:06:19,700
and we're going to keep these different zoom levels available to people,
118
00:06:19,700 --> 00:06:22,940
and for each one of those zoom levels as people zoom in the amount
119
00:06:22,940 --> 00:06:26,835
of data that's needed to store that is going to quadruple each time.
120
00:06:26,835 --> 00:06:31,250
Right? All of those map tiles at all of those zoom levels are being
121
00:06:31,250 --> 00:06:36,500
stored on the servers of the company that's providing this web mapping service.
122
00:06:36,500 --> 00:06:37,820
So, in this case,
123
00:06:37,820 --> 00:06:42,350
it could be Esri's cloud servers that are storing that data.
124
00:06:42,350 --> 00:06:44,890
So, when you are on your device,
125
00:06:44,890 --> 00:06:46,710
whatever it is: phone, tablet, laptop,
126
00:06:46,710 --> 00:06:49,890
desktop doesn't matter, and you're using their web servers,
127
00:06:49,890 --> 00:06:51,590
what's happening is that,
128
00:06:51,590 --> 00:06:57,530
when you ask to see a map of a certain area it's taking that request and sending it
129
00:06:57,530 --> 00:07:00,740
to the web map providers
130
00:07:00,740 --> 00:07:04,120
server and saying this is the part of the world that they're interested in.
131
00:07:04,120 --> 00:07:08,635
So, then it determines which tiles are needed at what map scale,
132
00:07:08,635 --> 00:07:12,230
and only sends you those tiles,
133
00:07:12,230 --> 00:07:14,750
and so that dramatically cuts down on the amount of
134
00:07:14,750 --> 00:07:17,220
data that needs to be sent at any given time, so,
135
00:07:17,220 --> 00:07:19,730
of course if you've got a limited amount
136
00:07:19,730 --> 00:07:22,665
of data on your data plan or bandwidth or whatever,
137
00:07:22,665 --> 00:07:27,110
might really speeds things up and that way the web mapping app is
138
00:07:27,110 --> 00:07:31,350
much more responsive and faster in terms of you being able to use it.
139
00:07:31,350 --> 00:07:32,955
So, that's why it's set up that way.
140
00:07:32,955 --> 00:07:35,060
Incidentally, if you're trying to get a sense of
141
00:07:35,060 --> 00:07:37,430
the amount of data we're talking about here,
142
00:07:37,430 --> 00:07:41,720
if you had to store all of the map data for
143
00:07:41,720 --> 00:07:47,170
the entire world at all zoom levels on your phone or let's say it's your phone,
144
00:07:47,170 --> 00:07:52,030
you would have to store 15 thousand terabytes of data.
145
00:07:52,030 --> 00:07:54,705
So, that's an enormous amount of data,
146
00:07:54,705 --> 00:07:56,420
phones are pretty fast, but they're not
147
00:07:56,420 --> 00:07:59,260
pretty powerful and lots of storage but not that much.
148
00:07:59,260 --> 00:08:02,000
So, that's why they have to come up with these strategies in order to
149
00:08:02,000 --> 00:08:04,630
only send you the data that's needed at any given time.
150
00:08:04,630 --> 00:08:09,670
But imagine having to store all that data even on a web server or Google or whatever,
151
00:08:09,670 --> 00:08:10,930
I mean all of these big companies.
152
00:08:10,930 --> 00:08:12,305
But that's a lot of data.
153
00:08:12,305 --> 00:08:18,170
Anyway, that's how web mapping works in terms of dividing up the world into
154
00:08:18,170 --> 00:08:20,240
these tiles so that they can
155
00:08:20,240 --> 00:08:24,895
scale and then you can zoom in and just see the areas that you're interested in.
156
00:08:24,895 --> 00:08:27,915
So, if we're looking at a web map,
157
00:08:27,915 --> 00:08:30,290
and we're trying to figure out what's the scale of that map,
158
00:08:30,290 --> 00:08:33,115
and if that varies depending on the device that we're using,
159
00:08:33,115 --> 00:08:37,520
or even just the size of the web browser on our desktop or whatever,
160
00:08:37,520 --> 00:08:39,740
if that's kind of dynamic or changing all the time,
161
00:08:39,740 --> 00:08:41,855
how do we calculate what the scale is of a map?
162
00:08:41,855 --> 00:08:46,140
Well, I'll just give you a quick demonstration of how this works.
163
00:08:46,140 --> 00:08:50,960
If you have a map at a given display size,
164
00:08:50,960 --> 00:08:54,445
you can measure it just like you would if it was a paper map.
165
00:08:54,445 --> 00:08:58,355
It doesn't matter whether it's on your tablet or your phone.
166
00:08:58,355 --> 00:09:00,680
Whatever it is that's the size of the area that's being mapped,
167
00:09:00,680 --> 00:09:03,664
we can just use a quick calculation to figure out the ratio
168
00:09:03,664 --> 00:09:07,130
of the map distance to the ground distance,
169
00:09:07,130 --> 00:09:09,590
and then we can calculate what the map scale is for that.
170
00:09:09,590 --> 00:09:10,760
So, we're just kind of doing
171
00:09:10,760 --> 00:09:13,740
the reverse calculation that we would normally do to figure out the distance,
172
00:09:13,740 --> 00:09:17,060
now we're going to use it to figure out the calculation for the scale.
173
00:09:17,060 --> 00:09:21,320
Right. So, if we are looking at a distance that we're interested in,
174
00:09:21,320 --> 00:09:23,730
and we want to know what the scale is for a particular area,
175
00:09:23,730 --> 00:09:28,435
if we know that there's a scale is a ratio of map distance to ground distance,
176
00:09:28,435 --> 00:09:36,205
and if I measured on my map that the distance for this blue arrow is 9.3 centimeters.
177
00:09:36,205 --> 00:09:37,830
Okay? Now, that just means,
178
00:09:37,830 --> 00:09:39,485
as long as you don't zoom in or out,
179
00:09:39,485 --> 00:09:41,880
whatever that, you just kind of left your map alone,
180
00:09:41,880 --> 00:09:43,410
and you've measured that distance,
181
00:09:43,410 --> 00:09:46,475
at that given moment at that display,
182
00:09:46,475 --> 00:09:48,140
that is the map scale,
183
00:09:48,140 --> 00:09:50,310
so you've got 9.3 centimeters.
184
00:09:50,310 --> 00:09:52,850
So, if this is an ArcGIS Online,
185
00:09:52,850 --> 00:09:56,570
I just use the measure tool to click on one end to the other.
186
00:09:56,570 --> 00:09:59,570
So, that's what is being shown here.
187
00:09:59,570 --> 00:10:01,210
So, the distance from here to here,
188
00:10:01,210 --> 00:10:05,515
and I just measured it with a measuring tool.
189
00:10:05,515 --> 00:10:09,765
That tells me that the distance is 69 meters.
190
00:10:09,765 --> 00:10:14,745
Okay. So, if we know that the distance on the map is 9.3 centimeters,
191
00:10:14,745 --> 00:10:19,815
if we know the distance on the ground is 69.0 meters, what's our map scale?
192
00:10:19,815 --> 00:10:24,990
Well, we just do one over x equals 0.093 meters over 69.0 meters,
193
00:10:24,990 --> 00:10:29,430
remember you have to use the same units in the numerator and the denominator,
194
00:10:29,430 --> 00:10:34,860
and then we solve for x and that gives us x equals 741.9.
195
00:10:34,860 --> 00:10:38,645
So, now we know that the map scale is one to 742,
196
00:10:38,645 --> 00:10:41,130
which is actually very large map scale.
197
00:10:41,130 --> 00:10:44,405
So, that's it. That's how you can calculate map scale.
198
00:10:44,405 --> 00:10:46,010
I don't know how often you would need to do it.
199
00:10:46,010 --> 00:10:47,300
Often, if you're using a web map,
200
00:10:47,300 --> 00:10:49,990
there's other ways to determine distances and things.
201
00:10:49,990 --> 00:10:51,790
But I think it's a useful if nothing else,
202
00:10:51,790 --> 00:10:54,230
is kind of a good mental exercise to make sure that
203
00:10:54,230 --> 00:10:57,940
the idea of map scale and how to calculate it is clear in your mind.17637
Can't find what you're looking for?
Get subtitles in any language from opensubtitles.com, and translate them here.