Recreating NCDC Covid-19 GIS Maps

Ever since the first case of Coronavirus disease (COVID-19) was announced in Nigeria on 27th of February 2020, the Nigeria Centre for Disease Control (NCDC) has in its effort to control the pandemic produced maps to document and visualize the status of the disease.

Some of these maps are part of the online 'COVID-19 Cases Tracking Dashboard' while other are included in pdf reports on 'update of COVID-19 outbreak' in Nigeria as seen below.

When you download and open one of the daily reporst, you will see the map below...

The second map is on the 'COVID-19 Cases Tracking Dashboard' web page.

The first map is a Choropleth map while the second is a Proportional Symbol map. In this article, I will reproduce these two maps. Lets get our hand dirty.

NCDC Choropleth map 

The data behind this map is available in the pdf file that contains the map. On the second page of the pdf file, you will see a table containing the map data that look like this below;

GENERAL FACT SHEET – DATA AS AT 9th SEPTEMBER 2020
Table 1: States with reported laboratory-confirmed COVID-19 cases, recoveries, deaths and days since last reported case

STATES	CONFIRMED CASES	DISCHARGED CASES	DEATHS	TOTAL ACTIVE CASES	DAYS SINCE LAST REPORTED CASE
TOTAL	NEW	TOTAL	NEW	TOTAL	NEW
Lagos	18,456	34	15,237	0	203	0	3,016	0
FCT	5,375	40	1,637	13	70	1	3,668	0
Oyo	3,209	8	1,961	0	38	0	1,210	0
Plateau	2,954	26	1,879	70	30	0	1,045	0
Edo	2,603	1	2,404	0	100	0	99	0
Kaduna	2,214	0	2,099	0	32	0	83	2
Rivers	2,195	2	2,087	12	59	1	49	0
Delta	1,780	12	1,616	13	48	0	116	0
Kano	1,728	0	1,604	0	54	0	70	2
Ogun	1,715	12	1,648	9	27	1	40	0
Ondo	1,575	9	1,485	42	33	0	57	0
Enugu	1,198	14	1,088	0	21	0	89	0
Ebonyi	1,034	4	986	0	30	0	18	0
Kwara	989	2	794	0	25	0	170	0
Katsina	819	0	457	0	24	0	338	2
Abia	816	0	712	0	8	0	96	2
Osun	803	1	756	2	17	0	30	0
Gombe	746	0	643	0	23	0	80	1
Borno	741	0	703	0	36	0	2	9
Bauchi	671	1	646	2	14	0	11	0
Imo	537	0	211	0	12	0	314	1
Benue	460	0	401	110	9	0	50	8
Nasarawa	443	2	298	0	12	0	133	0
Bayelsa	391	0	365	2	21	0	5	11
Jigawa	322	0	308	0	11	0	3	55
Ekiti	299	6	254	1	5	0	40	0
Akwa Ibom	283	0	247	0	8	0	28	1
Niger	244	0	216	0	12	0	16	5
Adamawa	230	2	180	0	15	0	35	0
Anambra	226	0	181	0	19	0	26	1
Sokoto	159	0	142	0	17	0	0	9
Kebbi	93	0	84	0	8	0	1	12
Taraba	91	0	73	0	6	0	12	2
Cross River	83	0	73	0	8	0	2	6
Zamfara	78	0	73	0	5	0	0	20
Yobe	67	0	59	0	8	0	0	41
Kogi	5	0	3	0	2	0	0	68
Total	55,632	176	43,610	276	1,070	3	10,952

States, including FCT, are arranged in descending order by number of total confirmed cases and then alphabetical order  

Now, copy this table into a spreadsheet and convert it to a CSV file. Note, you can also save it as an excel file, but here I don't want formating troubles so I will use a CSV file format.

Clean-up the data, the final result should look like this;-

Now, we will import this cleaned data into GIS software like QGIS and link it to a map of Nigeria (state level map). 

Join the shapefile map to the spreadsheet table and the result should look like below.

With this, we can visualize the spreadsheet data on the map. However, before we proceed with the mapping, there is a little problem we most fix.

By default, QGIS joined the table to the map by assuming that all the columns are of 'string' data type. That is not true in this case, so we most fix it. We will use the 'Refactor fields' tool from the processing toolbox.

So, go to the 'Processing' menu and select 'Toolbox', then search for 'Refactor fields' and use it to change the numeric fields to integer.

Complete the changes by running the 'Refactor fields' algorithm. A new updated map layer will be created. Now this is the map we will use for this visualization purpose.

Use the symbology property to create the choropleth map.

Add the state names as label and use the print layout to add other map elements such as scale, north arrow, legend as seen on the pdf sample.

That is it as seen below.

The resulting map provided here may not be 100% exactly like that of NCDC, but at least we are very close and with a little more tweaking here and there, we can make it look perfectly the same.

Lets move to the second map.

NCDC Proportional Symbol map

Here we will use the same cleaned CSV data from above and as you may have already noticed, this map use a point features layer instead of polygon.

So, we have to prepare the point layer to represent the states not polygon. We can use the centroid of the states polygon to archieve this or we can get the latitude and longitude values of the capital of each state.

Here I used the geometry functions 'x($geometry)' and 'y($geometry)' in field calculator to generate a new attribute with longitude and latitude of the centriond fro each state polygon. Then export the attribute as CSV and imported is back a point layer using the 'Add Delimited Text Layer' tool.

After import the point layer, note that I used the OpenStreetMap plugin to add a background map so that we can have something close to the NCDC map we are trying to reproduce.

After you installed the OpenStreetMap plugin, it will available under web menu as seen below.

To create the proportional symbol map, there are two way of doing it namely:-

1) Use graduated symbology and change the method to 'Size' instead of 'Color'

2) Use data override function on single symbology

To access this go to: 'Data defined override' botton the select 'Assistant...'.

Each method has is pros and cons, but at the end you will achieve same proportional symbol map as seen below;-

Note:

• The dataset used here may not be the actual reflection of COVID-19 status in the country, it is merely for explanation sake.
• The second map is left in static form instead of dynamic web map as seen on NCDC website. If you want to take the static map further to the web, consider using the qgis2web plugin.

At the end, I hope you got something useful out of this post.

Happy mapping!