Assessing Interannual Urbanization of China’s Six Megacities Since 2000
Round 1
Reviewer 1 Report
This is an interesting paper.
Author Response
Dear Review,
Thank you very much for all constructive suggestion you provide for our manuscript. Thank you very much for your accepting our revised manuscript.
Reviewer 2 Report
For the revised version the authors have carefully commented on the comments of the reviewers. Unfortunately, not all of these answers to the reviewers questions have been included in the new version of the paper.
Anyway, the paper has been improved substantially. Also the English has been revised.
The paper is now in a form which is acceptabel for publication.
Author Response
Dear Reviewer,
Thank you very much for all constructive suggestion you provide for our manuscript. Thank you very much for your accepting our revised manuscript. We have modified our manuscript again, we think it better now.
Reviewer 3 Report
The paper I reviewed is the re-submission of remotesensing-519937. I recommended the article for major review, clearly stating that the report was negative and substantial work was needed. In this resubmission the author improved to some extent the paper based on the three review reports.
the authors significantly improved the presentation of the findings, remarkably 4.2 and the discussion part. also the English language has improved making the reading more efficient.
However, the procedure to extract urban land is not sufficiently detailed. despite the state of the art moving towards automatic workflows, the expert based visual interpretation is not negative per se. In the paper the authors should make an effort to list all the relevant parameters that state of the art visual interpretation is based upon (see dedicated manuals). few trivial questions:
is the position error reported a good quality metric is the extraction based on a single expert judgment is the expert trained/instructed to discern between marginal spectral differences in partially built-up pixels is this systematic across the 6 megacities which interpretation symbols were provided is 30+ m resolution suitable to visually delineate built-up area annually did interpreters classify individual 30+ m pixels for the 18 years over the 6 megacitiesValidation does not appear as a word in the text. how accuracy >90% can be claimed, which indicators were used, which reference map, geospatial layer or carthography was used, does this apply to all the 6 megacities and all years? how >90% accuracy is achieved in Tianjin 2003, Guangzhou 2005 etc. (from supplementary table 1). could you also specify how suppl. table 1 aligns to line 71 and the novelty of the research.
are figures in km2 reported in 4.1 aligned with the precision of the experiments
other elements to consider, line numbers in parenthesis
(36) rational urban planning is a specific and contextualized practice/movement in urban planning discipline. are authors referring to that disciplinary positions? recent directions of planning guidelines (see UN-Habitat) do substantially shift away from the rationalist positions.
(82) not sure the ref. to table 2 is appropriate, isn't it table 1
(94) what is urbanization rate in percent meaning?
Table 1, to which year is the population referring to ?
(168) typo
figure 4 caption, (b) what is a proportion of expansion?
(275) section 4.3 refers to allometric relationship between urban land and population dynamics. should the process be labelled as such when shapes grows more than the population? is it in line with the biological connotation of the term? in the SDG 11.3.1 context is this in line with the achievement of the goal? see also (347)
also on 4.3 the discussion completely overlooks population density, that is a key characteristics of cities and megacities in particular
across the text the acronyms should be explained when they first appear (116) LST and VC even if they are established terms. Same applies to the conclusion (especially the expansion types should be written explicitly)
I hope the authors recognise the need for clear workflows to extract features from remote sensing as a key principle of the discipline. the article is interesting but all built upon unknown processing.
Author Response
Answer to Reviewer 3:
Thank you very much for the time you invested to improve our manuscript. We think it supported very much the improvement of the second version of the manuscript. Here are our detailed answers to your comments:
Comments and Suggestions for Authors: The paper I reviewed is the re-submission of remotesensing-519937. I recommended the article for major review, clearly stating that the report was negative and substantial work was needed. In this resubmission the author improved to some extent the paper based on the three review reports.
The authors significantly improved the presentation of the findings, remarkably 4.2 and the discussion part. also the English language has improved making the reading more efficient.
Response: Thank you for your comments of the second version of our manuscript.
However, the procedure to extract urban land is not sufficiently detailed. despite the state of the art moving towards automatic workflows, the expert based visual interpretation is not negative per se. In the paper the authors should make an effort to list all the relevant parameters that state of the art visual interpretation is based upon (see dedicated manuals). few trivial questions: ① is the position error reported a good quality metric is the extraction based on a single expert judgment is the expert trained/instructed to discern between marginal spectral differences in partially built-up pixels is this systematic across the 6 megacities which interpretation symbols were provided is 30+ m resolution suitable to visually delineate built-up area annually did interpreters classify individual 30+ m pixels for the 18 years over the 6 megacities. ② Validation does not appear as a word in the text. how accuracy >90% can be claimed, which indicators were used, which reference map, geospatial layer or carthography was used, does this apply to all the 6 megacities and all years? how >90% accuracy is achieved in Tianjin 2003, Guangzhou 2005 etc. (from supplementary table 1). could you also specify how suppl. table 1 aligns to line 71 and the novelty of the research. ③ are figures in km2 reported in 4.1 aligned with the precision of the experiments.
Response: Thank you for your constructive suggestions. Visual interpretation and automatic classification are two major approaches to extract urban lands and other land use/cover types. Generally, automatic classification methods are based on different rules and parameters. However, visual interpretation mainly depends on the professional knowledge and experience. Sometimes, the results of visual interpretation maybe affected by the proficiency levels of technicians. Therefore, the quality control is necessary.
As visual interpretation has been widely applied (especially by early remote sensing scientists and technologists), it has become a relative mature technique now. Apart from the professional background and interpretation ability of those researchers, a series interpretation symbols for land use/cover types are also necessary to reduce the error caused by the interpretation of technicians. Our team has been working on visual interpretation for a long time. Each interpreter has been committed to visual interpretation works for at least 10 years. We summarized some interpretation symbols for the land use/cover types in our previous publication (as shown in the following figure). The symbols are built in accordance with different elements in remote sensing image, including size, shape, color, hue, texture, and shadow, etc.
Figure. Case interpretation symbols for each land use/cover type. (Note: This figure is cited from Zhang et al. (2014a).)
Quality control is composed of two parts: repeated interpretation by different professionals and field verification. When employing repeated interpretation, apart from the interpretation symbols, some auxiliary materials including Google Earth platform and topographic maps were also referred to. When employing verification, we took photos and recorded the situation of local land use/cover on tables, especially recording the impact of ecological and environmental engineering and urbanization process on land use/ cover. The former was employed to each interpretation product, while the latter was employed mainly in 2000, 2005, 2008, 2010 and 2015. If the accuracies of urban lands were lower than 90%, the remotely sensed images should be re-interpreted. Based on these symbols and quality control methods, our team has completed a series of land use/cover products. Among which, the urban maps have been widely used and their accuracy and feasibility have been proven by many publications (i.e., Liu et al.,2016; Wen et al., 2016, Zhang et al., 2014b). In this study, we used the urban lands of China’s six megacities, which were just a part of these products. However, the visual interpretation is a sophisticated process and needs quiet a long content to detailed illustrate. As we have specially written a literature (Zhang et al., 2014a) to describe its procedures in detail, we citied this literature and briefly listed the steps in the revised manuscript. Besides, we have inserted the interpretation symbols to Figure 2 of our revised manuscript.
In addition, the Appendix. Table 1 has showed the years of remotely sensed images used to delineate urban lands. As introduced in Section 3.1, the basic principal of selecting images is less than 10% cloud cover and vigorous vegetation growth, not all years could obtain such images. We have said in Line 147-150 of the manuscript, “given the difficulty in obtaining high-quality remotely sensed images of China’s six megacities in some years, the interpolation data on urban land areas in these years were applied as a supplement by executing the method of Liu et al. (2016)”.
Besides, Section 4.1 elaborated the basic characteristics of urban expansion in China’s six megacities. The relevant values in km2 were the results aligned with the precision of the experiments.
We hope the re-organized Section 3.2 read better now.
References:
Zhang, Z.; Wang, X.; Zhao, X., etc. (2014a). A 2010 update of National Land Use / Cover Database of China at 1: 100000 scale using 474 medium spatial resolution satellite images. Remote Sensing of Environment, 149, 142–154.
Liu F., Zhang Z., Wang X. (2016). Forms of Urban Expansion of Chinese Municipalities and Provincial Capitals, 1970s–2013. Remote Sensing, 8, 930.
Wen, Q., Zhang, Z., Shi, L., etc. (2016). Extraction of basic trends of urban expansion in China over past 40 years from satellite images. Chinese Geographical Science, 26(2), 129–142. doi:10.1007/s11769-016-0796-z.
Zhang, Z.; Zhao, X.; Liu, F., etc. (2014b). Atlas of urban expansion by remote sensing in China, Star Map Press: Beijing, China.
(36) rational urban planning is a specific and contextualized practice/movement in urban planning discipline. are authors referring to that disciplinary positions? recent directions of planning guidelines (see UN-Habitat) do substantially shift away from the rationalist positions.
Response: Sorry for our unclear expression before. We meant that studies about urbanization processes could enriched the existing materials. And the researching results could serve as references when designing urban planning. We have changed the original sentences to “Researches of the urbanization processes could provide basic materials as references when designing rational urban planning” in Line 36 of the revised manuscript.
(82) not sure the ref. to table 2 is appropriate, isn't it table 1
Response: Thank you very much for your careful reading and reminding. Yes, it should be Table 1 here. We have changed “2” to “1” in Line 82 of our revised manuscript.
(94) what is urbanization rate in percent meaning?
Response: Urbanization rate is defined as the proportion of urban population in the total population, and it’s regarded as an important indicator of urbanization (National bureau of statistics of the People’s Republic of China, 2019; United Nations, 2019).
National bureau of statistics of the People’s Republic of China. The 2018 statistical communique on national economic and social development; Beijing, 2019.
United Nations, U. World Urbanization Prospects 2018; New York, 2019.
Table 1, to which year is the population referring to ?
Response: As we all know that most countries generally execute national population census in exact years. In China, a total of six national population censuses based on administrative levels have been conducted in 1953, 1964, 1982, 1990, 2000, and 2010, respectively. These censuses are authoritative and reliable, and have been widely used to divide Chinese cities into various levels (i.e., megacities, big cities, small cities, etc.). Hence, the newest sixth national population census of six megacities were shown in Table 1. We have added its corresponding year in Line 102 of our revised manuscript.
(168) typo
Response: Thank you for your reminding. We have changed it to “Researches about the cotemporary evolution of these indicators could help further understand the urbanization process of China’s megacities.” in Line ** of our revised manuscript.
figure 4 caption, (b) what is a proportion of expansion?
Response: Urban lands in China’s megacities expanded from 2,810.77 km2 in 2000 to 7118.77 km2 in 2018. The total areas of newly developed urban lands were 4308.00 km2. The expansion proportions indicate the contributions of each megacity to the total expanded areas. To avoid misunderstanding, we have changed “expansion proportions” to “contribution rates to total expanded areas” in Line 180-181 of our revised manuscript.
(275) section 4.3 refers to allometric relationship between urban land and population dynamics. should the process be labelled as such when shapes grows more than the population? is it in line with the biological connotation of the term? in the SDG 11.3.1 context is this in line with the achievement of the goal? see also (347), also on 4.3 the discussion completely overlooks population density, that is a key characteristics of cities and megacities in particular
Response: Thank you for your question. In the original manuscript, we used “allometric” in accordance with several previous publications, which might not be written rigorously enough. Based on your kind reminding, we have looked up the biological connotation of the term. We’re sorry for wrongly applying the word “allometric” in the original manuscript. We have deleted the word in Line 287 and Line 358-359 of the modified manuscript. The goal of SDG 11.3.1 is to make cities and human settlements inclusive, safe, resilient and sustainable. However, urban land-population-GDP of China’s six megacities presented different growth speeds at present, therefore, going against the goal. As China is still a developing country, the results of this work are relatively reasonable and also in line with the results of some previous researches. In addition, this phenomenon could be ascribed to the special urbanization process of China to some extent. There are also some publications, which have explained this process. We have said in the last sentence of the Discussion Section, “obtaining sustainability in China’s cities is an expected achievable goal that requires the joint efforts of the government and ordinary people”. Besides, in this paper, we emphasized on four tasks as introduced in the Introduction Section. These above-mentioned tasks could not thoroughly reflect the characteristics of megacities, because urbanization in megacities involve various aspects. For instance, as for the third task, we mainly compared the growth rates of urban land-population-GDP but overlooks population density. In term of this problem, we have added some sentences in Discussion Section to make it more comprehensive. We hope it better now.
across the text the acronyms should be explained when they first appear (116) LST and VC even if they are established terms. Same applies to the conclusion (especially the expansion types should be written explicitly)Response: Thank you for your reminding. The LST and VC first appeared in the last sentence of Introduction Section along with their explanations (Line 79 of our revised manuscript). Types A, B, C and D first appeared in Section 3.3 along with their explanations (Line 171-172 of our revised manuscript). In addition, we have change “Types A and D” to “Two expansion types — loose expansion at high speed and compact expansion at low speed —” in Line 391-392 of our revised manuscript, changed “VCs” to “Vegetation coverages” in Line 396 of our revised manuscript, and changed “LSTs” to “Land surface temperatures” in Line 397 of our revised manuscript.
I hope the authors recognise the need for clear workflows to extract features from remote sensing as a key principle of the discipline. the article is interesting but all built upon unknown processing.
Once again, thank you very much for all constructive suggestions and reminding. They not only helped so much to modify this manuscript, but also helped us to develop good writing habits. We think these suggestions will play important roles in our future researches.
Author Response File: 
Author Response.docx
Round 2
Reviewer 3 Report
In this round of review, the authors did a remarkable improvement to the paper, making it suitable for publication, and making it a valuable piece of research.
in particular, as stated by the authors, the clarifications made in section 4.2 are essential to reconcile the visual interpretation approach that "mainly depends on the professional knowledge and experience" to the scientific practice of thorough explanation of research experiments and a self explanatory piece of research as the paper now is.
Related to point 5 of the point by point rebuttal, for a disambiguation reason, I discourage to refer to urbanization rate.in the WUP: The rate at which the percentage urban grows or declines is called the urbanization rate (WUP 2018 p.47). Proportion/percentage is more suitable and aligned to WUP terminology.
in general the paper in its present form is very much improved and in recommending it for publication, I praise the authors for their engagement with the thorough review.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
This paper is of general interest but it's main purpose of categorizing the mega cities into four types s flawed. The measure of are and perimeter must be highly correlated, so either category D or A must always occur, except for random error. Further, the fact that vegetated area declines as urban area increases is an effective tautology and not interesting as a finding.
Other problems are present:
1) the references made in the first paragraph (and elsewhere) are not really relevant/appropriate, e.g.1,2 for urban population change. Why is a reference (3) needed for the second sentence?
2) p.2, l. 47 - how are megacities "representative"?
3) p. 2, l. 70 "remotely sensed satellites"?
4) Part 2 lists latitudes and longitudes, which are not important, but not populations, which are important.
5) p. 2, l. 94 - implies magacities are typical (reflect)
6) p. 4 Why are GRA and GRI given as abbreviations but not used in eq. 1 and 2, respectively? Also see line 151 and eq. 3 and 4.
7) l. 131 "standardizing" not "normalizing"
8) l. 141 - "inexistent"?
9) l. 149, household-registered populations are not actual city populations
10) Why is eq. 7 appropriate?
11) p. 6. l. 191 - What is "dispersion"?
12) Fig 5 should be a histogram; it is misleading as given
Reviewer 2 Report
English has to be improved. Though there are only a minor number of spelling and grammar errors, the English is clumsy and incorrect/misleading terms are used. Some examples: line 41: promoting the formation of megacities line 47: when reflecting the urbanization characteristics line 65: their performance under urbanization effects line 70: Remotely sensed satellites remote sensing satellites More example could be added throughout the whole text. Maybe an automated translation program has been used? Data quality is of high importance for the interpretation of the results. The information given in 3.1. about the imagery data is not enough to judge the quality of the results. E.g. it is mentioned that the spatial resolution is 30-80m, which means a pixel area of 0.0064 sqkm. On the other hand, all the results are given in the same range of accuracy, i.e. 0.01 sqkm. Thus a misinterpretation of only one pixel will result in different results! My point is, all the result values should be rounded to some realistic values. Fig 2 shows that all the images have been interpreted manually?! That is really not state of the art! So the results are very doubtful, as also not idea about the classification accuracy is given. Is there no quality check performed? The results obtained e.g. in Fig. 5 are very doubtful. How much of the amplitudes is due to misinterpretation, how much is really land use change? Some of the formulae are rather trivial, but even though repeated over and over again (1,2,3,4) This is not appropriate for a scientific paper. To normalize the results, it would be better to mention the (I suppose again a very simple formula then to point to SPSS! Formula 6 and 7 are both using Ni but the parameter has different meaning. This should be changed. Table 1 should be transferred to some diagram for easier grasping. Some of the results e.g. in 4.4 are not properly explained, some are trivial again and not worth mentioning here. Just doing it, because there is data available is not very scientifically sound. Not all the conclusions are covered by the results, e.g. the context of one child or two child policy in the context of urbanization. These conclusions seems to be misplaced in this context.
Reviewer 3 Report
The paper proposes an analysis of the spatial expansion of 6 megacities in China in the period 2000 – 2018 combining satellite scenes from different sources, also including demographic, economic and ecological indicators.
The research in its current form is not suitable for publication. The research design is not sufficiently clear and developed (eventually too rich), the presentation of the research findings are not clearly prioritized (several interesting facts are presented, but not clearly organized), and the remote sensing connotation of the study is absent. In addition, English editing is necessary to help the reader follow the argumentations.
I have two main concerns, the first, related to the need of clear organization of research findings and interconnection among them and overall research presentation, as is, the paper contain a lot of materials that do not convey messages; second the remote sensing component is largely overlooked. (numbers in brackets are manuscript lines).
Below some options to substantially improve the paper:
In the introduction, authors affirm (point 1), that existing research is mostly single city (i.e. 57 – 59) but in the paper, it is not clear how the comparative analysis of the 6 case studies emerge. Points 2 and 3 are addressed in the paper but not critically discussed.
introduction can more clearly introduce urban and urbanization analysis with remote sensing.
Section 2 is complex to follow. A table summarizing the study areas is more suitable. Section 3 should summarize the process designed by [ref. 34], the semantics in Mohurd 1991 and Shi et. al. 2015.
4.1 is a rambling paragraph (also 191 – 200, 204 – 237 too). Here authors could compare the patterns of megacities with 6 megacities average and min max growth, using a chart with sectors (above below average of relative land area expansion). GRP is not used (how would Shenzhen and Guangzhou perform compared to different forms, i.e. Shanghai or Beijing?).
Table 1 should be presented as a chart (of relative expansion by type in each of the cities), is it a dominant land expansion?
Sentences like 204 – 206 are frequent in the paper, authors should make an effort to find alternative ways to present such findings, eventually with charts, but in a clear way, easing the reading (it’s easy to get lost).
Fig. 7 should be presented with reference to population density, in this form it does not clearly present facts.
4.4 should be presented in function of expansion types introduced in fig. 1.
The discussion section is too largely bound to the legacy/history of the cities, how the indicators instead characterize the different types of land expansion?
The population change and land expansion is addressed in SDG 11 indicator, how this research is salient to yours? https://0-doi-org.brum.beds.ac.uk/10.3390/ijgi8020096
In terms of remote sensing/methodology: clear metadata and features of scenes has to be indicated. Which workflow was used? Summarize. Which visual interpretation was done?
(132) which normalization took place?
Below some options to improve the paper for publication:
(11 – 13) and (23 – 24) language improvement required
(37 – 38) reference to the UN 2030 Development Agenda would give more appropriate context
(42 – 43) why WUP 2014, does the 2018 update introduce differences, which, citation formatting needed
(50) ref. formatting
(70) satellites ?
(79 – 95) as a table, quantify the proportion of national territory, and to what extent megacities reflect China urbanization (is it driven by large or medium cities, see WUP 2018)
Figure 1, coordinates of the bounding box should not include the case studies, Beijing isn’t at 40E 40N; expanded urban land 2000 – 2018 could also be classified (option), are the case studies with the same scale? Caption to be expanded.
(100 – 109) a table with key metadata (including frequency distribution of scene acquisition –year/month) should be provided as in the state of the art research.
Equations (1, 2, 3, 4) no need to introduce new acronyms use GRA not Ga, it is not required and also confusing
(134) change numbers to two digit codes
(135) what is a high level of GRA and GRP (why GRP does not appear in results?)
(156 – 162) what is R1 and R2 mentioned in 270? Should be explained here
(166) typo
(166 – 169) how pixel values are translated into city-wide values?
Fig 6. It would deserve a paragraph focusing on the differences between cities
(249) typo
Fig 8. Should be square charts
Section 4.4 are findings in line with literature of greenness in urban centers? Address in discussion
Reformulate conclusion making them clearer, expansion types should be written in the extended way, not clear otherwise. Select parts of the discussion to improve it and make it more systematic.
