# Analysis of Coastal Zone Data of Northern Yantai Collected by Remote Sensing from 1990 to 2018
## 3 Results
### Characteristics of Coastline Changes
#### 3.1.1 Variation of Coastline Length
Among the cities studies, Laizhou, Longkou, and Penglai have the largest increase in artificial boundary lines, which are 81.91 km, 58.07 km, and 61.02 km, respectively. The main reason is that the impact of human activities such as the construction of ports, artificial islands, and coastal areas is increasing, which makes the coastline extend towards the sea and thus lengthen. The increase of the artificial boundary line is not only the extension of the artificial boundary line to the sea but also the transformation of the natural boundary line. Many areas, led by Laizhou, have built sunshine ponds and aquaculture ponds on the muddy coast, thus transforming the natural boundary line into the artificial boundary line. The total length of the natural boundary line continuously decreased. Longkou's natural coastline decreased by 29.13 km, accounting for 48.20%. The natural coastline of Zhaoyuan has been reduced the least with a total decrease of 0.22 km, accounting for approximately 1.72%. Figure 4: Change of coastline length in the study area from 1990 to 2018. \begin{table}
\begin{tabular}{c c} \hline \hline
**Time Slot** & **Coastline Change Intensity/\%** \\ \hline
1990–2000 & 0.84 \\
2000–2010 & 1.13 \\
2010–2015 & 3.47 \\
2015–2018 & 0.39 \\
1990–2018 & 1.54 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Strength of coastline length change. Figure 5: Variation of first class coastline length in different regions from 1990 to 2018. (**a**) Change of coastline length in Laizhou, (**b**) Change of coastline length in Zhaoyuan, (**c**) Change of coastline length in Longkou, (**d**) Change of coastline length in Penglai, (**e**) Change of coastline length in Fushan, (**f**) Change of coastline length in Zhifu, (**g**) Change of coastline length in Laishan, (**h**) Change of coastline length in Muping, (**i**) Change of total length of coastline in study area. From 2015 to 2018, the natural boundary length of the coastline in the study area decreased from 202.79 km to 21.13 km, a total of 1.66 km. The length of the artificial boundary line increased from 387.53 km to 396.47 km, an increase of 8.94 km. The change of the estuary boundary line is negligible. However, the natural boundary lines of some counties and municipalities had an increasing trend, while the artificial boundary lines had a decreasing trend. Among them, the length of the natural boundary line in Longkou increased by fluctuation, decreasing from 31.32 km to 30.52 km, and then increasing to 31.33 km. The length of artificial boundary lines in Fushan and Mouping decreased by 0.38 km and 0.13 km, respectively. The main reason is that in recent years, with the implementation of the major strategy of the Blue Economic Zone in Shandong Peninsula, in order to make better use of marine resources and develop the marine economy, the relevant departments have strengthened their control over the abuse of marine resources in violation of regulations, and have also strictly examined the approval of the construction and development of various ports and wharfs. The growth rate of the coastline has slowed down, and the quality of the marine environment has improved. According to the secondary coastline data of the Yantai northern region from 2015 to 2018, it can be seen that the length of the coastal construction boundary line, port and wharf boundary line, road boundary line, protection engineering boundary line, breeding boundary line, gravel, and sand boundary line, and silt boundary line have increased. The increase was 7.45, 5.62, 5.33, 2.71, 0.91, 0.86, and 0.05 km, respectively. The length of the other artificial boundary lines, bedrock boundary lines, estuary boundary lines, and salt field boundary lines decreased by 2.78, 2.45, 0.09, and 0.02 km, respectively. Among them, the coastal construction boundary lines in Zhifu, Penglai, and Fushan increased the most, from 0, 5.43, and 11.42 km in 2015 to 2.37, 7.27, and 13.23 km in 2018, respectively.